ELECTRICITY

 

ELECTRIC CHARGE:

Object normally contain equal numbers of protons and electrons. A negatively charged object has more electrons than protons; and a positively charged object has more protons than electrons (deficiency of electrons).

The net charge on an object is measured en coulombs (C). This is the S.I. unit for charge and it is defined below.

 

ELECTRIC CURRENT:

A current is a flow of charge.

Electric current is the flow of  charged particles around a circuit of conducting material such as metals. In a metal wire many electrons are free to move, so that a current can flow in a metal wire as a flow of electrons.

The rate of flow of electric charge is called "CURRENT".

I means the current between two points. It is the charge which flows/time taken.

Current size (I) is a basic quantity. The unit for current is the ampere (A) in the S.I.


Current size is related to charge (Q) moving through (entering and leaving) a wire in time (t) by:

And 1 A (ampere) = 1 C(coulomb)/s

 

ELECTRIC CIRCUIT:

To make a steady direct current flow in a simple electric circuit we need two main componentes:

1. A source of electric potential (e.g. cells or battery): A power supply like a cell or battery.

2. An energy-consuming device (e.g. a resistor). You must join the two terminals (+ and - ) to a continous closed loop of contuctors. One of these conductors may be a light bulb, a buzzer, or some other device you wish to use. A switch can make or break contact with a loop of conductors, and no current flows if the loop is not complete. The complete loop of comoponents is called circuit.

 

Current is  flow of negatively charged electrons from the negatively charged terminal to the positively charged terminal of the electrical supply. However, the conventional direction of current flow is usually shown by an arrow opposite to that of the electron flow. The direction of current flow and electron flow are opposite.

In a conventional current  flow goes from the cellīs positive terminal to its negative terminal.

 

CELLS AND BATTERIES:

The energy given to the electrons to push them round an electrical circuit is transferred from electrical sources such as batteries, solar cells and generators to components in a circuit, such as lamps, resistors, bells, motors, LEDs and buzzers. The energy transferred makes things happen in the circuit such as light, heat and sound.

Cemical cells can be made with two different metal electrodes dipping into varios ionic solutions.

The chemicals react with one another, causing an electric current to flow through the cells. Thus chemical energy is again transformed into electrical energy as the reactants are changed into chemical products of the reactions.

Group of cells connected together are  called batteries. They provide the electromotive force (e.m.f) which drives electric current. We can measure emf in volts (V) by connecting a voltmeter to a cell.

Rechargeable batteries are those in which the chemical process from reactants to products can be reversed by driving a reverse electric current through the battery.

 

 

POTENTIAL AND POTENTIAL DIFFERENCE:

The  potential of a place may be thought of as its attractiveness for electrons and unattractiveness for positive charge. A place where there is a high concentration of electrons or which has a lot of electrons near it will have a low potential.

 

The difference of potential (PD) V between two places is defined as the work done W per coulomb of charge moved from the one place to the other.

V= W/Q

Where  W is the work done (if positive charge Q moves from lower potential to higher potential, from - to +) or energy obtainable from the movement (if negative charges goes from - to + place).

The unit for PD is the volt (V).

 

The potential of a place measured in volts is the PD between the place concerned and some reference point.

 

Electric current flows spontaneously from a higher potential place (+) to a lower potential place (-) if the two places are joined bya a conducting path.

 

OHMīS LAW:

This law states that the current I through a given conductor is proportional to the PD between its ends, provided that  its temperature does not change: V/I = constant.

 

RESISTANCE "R" OF A CONDUCTOR:

This is the opposition of the conductor to current flow through it. It is defined as the Potential Difference needed across it (between its ends) per ampere of current.

                               R= V/I

The unit for resistance is the ohm (W).

 

RESISTORS:

These are device for providing resistance to the flow of current. Some variable resistors are called rheostats.

A thermitor is a temperature sensitive resistor.

 

RESISTIVITY "r " OF A MATERIAL:

The resistance R of a conductor is proporcional to its length, inversely proportional to its area of cross-section A, and dependent upon the nature of the material, described by its resistivity r.

                               R= r.l/A

 

 

ELECTRIC CIRCUIT:

Often a current is produced by use of a votaic cell or battery (two or more cells joined together). The cell creates and mantains a PD between its terminals.

A currente is obtained if these two terminals are joined by a conducting path, i.e. when a complete circuit is formed.

SCHEMATIC DIAGRAMS

This section lists the main components of d.c. (direct current) circuits that you will encounter in your physics classes.

This is a source of emf (electromotive force), with a voltage of , measured in units of volts, V. The most common source you will see will be a battery.

This is a resistance, measured in units ohms (W), . Most often it will be a resistor. However, wires connecting parts of a circuit are really not resistance-free. We can model this real-life case by putting a 'resistor' in the circuit which has the same resistance as the wires would have. Thus the wires can still be considered resistance-free since their resistance is represented by an additional resistor.

 

This is a capacitor, with capacitance C measured in units of farads, F. The perfect capacitor will have no resistance (or inductance; see next), and we will assume that this symbol represents such an ideal capacitor. If a capacitor is not ideal, that is, it has some resistance (or inductance) associated with it, then we can model this by putting a 'resistor' (or inductor) in parallel with the capacitor. This resistor (or inductor) will have the same resistance (or inductance) as the non-ideal capacitor.

This is an inductor, with inductance L, measured in units of henrys, H. To model a non-ideal inductor in a circuit (an inductor with an associated resistance or capacitance) we can put a resistor in series or a capacitor in parallel with the inductor. Giving these the same values as the inductor will represent an imperfect inductor.

 

 

 

DC Circuits

 

RESISTORS IN SERIES

Resistors can be connected in series; that is, the current flows through them one after another. The circuit in Figure 1 shows three resistors connected in series, and the direction of current is indicated by the arrow.

 



 

 

 

 

 

 

Figure 1 Resistors connected in series.

Note that since there is only one path for the current to travel, the current through each of the resistors is the same.


Also, the voltage drops across the resistors must add up to the total voltage supplied by the battery:


Since V = I R, then


But Ohm's Law must also be satisfied for the complete circuit:


In general, the equivalent resistance of resistors connected in series is the sum of their resistances. That is,


 

RESISTORS IN PARALLEL


Resistors can be connected such that they branch out from a single point (known as a node), and join up again somewhere else in the ciruit. This is known as a parallel connection. Each of the three resistors in Figure 1 is another path for current to travel between points A and B.


Figure 1 Example of a circuit containing three resistors connected in parallel


Figure2 Circuit containing resistors in parallel, equivalent to Figure 1


Note that the node does not have to physically be a single point; as long as the current has several alternate paths to follow, then that part of the circuit is considered to be parallel. Figures 1 and 2 are identical circuits, but with different appearances.

At A the potential must be the same for each resistor. Similarly, at B the potential must also be the same for each resistor. So, between points A and B, the potential difference is the same. That is, each of the three resistors in the parallel circuit must have the same voltage.


Also, the current splits as it travels from A to B. So, the sum of the currents through the three branches is the same as the current at A and at B (where the currents from the branch reunite).


And the equivalent resistance will be:

 


 

 

 

 

 

http://www.glenbrook.k12.il.us/gbssci/phys/THender/quizzes/u8/q191.html

ELECTROSTATIC Quiz#1

Part 1: FIll in the Blank

 

1. A neutral object becomes ________________ charged if electrons are removed.

2. Unlike charges _______________ one another.

3. _______________ are materials with a conductive capacity between conductors and insulators.

4. The process of charging a neutral body by touching it with a charged body is called charging by ________________.

5. Charges added to a(n) _______________ will immediately spread throughout the body.

6. Charges added to one part of a ________________ will remain in that part.

 

Part 2: Multiple Choice

Choose the one best answer to the following questions. (1 pt. each)

1. Two like charges ________.

a.        attract each other

b.        repel each other

c.        neutralize each other

d.        have no effect on each other

e.        must be neutrons

2. Protons and electrons ____________.

a.        repel each other

b.       attract each other

c.        do not interact

3. The electrical force between charges is strongest when the charges are __________.

a.        close togethere

b.        far apart

c.        the electric force is constant everywhere

4. If you comb your hair and the comb becomes positively charged, then your hair becomes __________.

a.        positively charged

b.       negatively charged

c.        uncharged

5. A conductor differs from an insulator in that a conductor ________.

a.        has more electrons than protons

b.       has more protons than electrons

c.        has more energy than an insulator

d.       has faster moving molecules

e.        none of these

6. A negatively charged rod is brought near a metal can that rests on a wood table. You touch the opposite side of the can momentarily with your finger. The can is then _______.

a.        positively charged

b.       negatively charged

c.        uncharged

d.       charged the same as it was

7. An electroscope is charged positively as shown by foil leaves that stand apart. As a negative charge is brought close to the electroscope, the leaves _________.

a.        fall closer together

b.       spread apart further

c.        do not move

8. Two charges separated by one meter exert a one N force on each other. If the charges are pulled to 3 m separation distance, the force on each charge will be ________.

a.        0.33 N

b.       0.11 N

c.        0 N

d.       3 N

e.        9 N

9. Two charges separated by one meter exert a one N force on each other. If the magnitude of each charge is doubled, the force on each charge is _________.

a.        1 N

b.       2 N

c.        8 N

d.       4 N

e.        none of these

10. A positive charge and a negative charge held near each other are released. As they move, the force on each particle __________.

a.        increases

b.       decreases

c.        stays the same


Part 3: Problem-Solving

 

To receive credit for the following problems, show some work.

1. A hydrogen atom contains a proton and an elctron separated by a distance of 5.0 x10-11 meters. The charge on the proton is the same as the charge on the electron: 1.6x10-19 C. Calculate the force of attraction between the two particles.

2. A positve charge of 1.8x10-6 C and a negative charge of -1.0x10-6 C are 0.014 m apart. What is the force between the two particles?

3. Two charged objects have a repulsive force of .020 N. If the charge of one of the objects is doubled, then what is the new force?

4. Two charged objects have a repulsive force of .04 N. If the distance separating the objects is halved, then what is the new force?

5. Two charged objects have an attractive force of .02 N. If the charge of one of the objects is halved, and the distance separating the objects is doubled, then what is the new force?

6. Two charged objects have a repulsive force of .020 N. If the charge of both of the objects is doubled and the distance separating the objects is doubled, then what is the new force?

 

Part 4: Correcting False Statements

The following statements are false. In three complete sentences or less, explain what is wrong with the statement and correct it.

1. Object A is positively charged and Object B is electrically neutral. When object A touches Object B, protons are transferred from Object A to Object B.

2. If an electroscope is touched by a charged object, the leaves will diverge. However, when the object is drawn away, the leaves will relax to their original rest position.

3. Object A is positively charged. Object B is an electrically neutral insulator. If Object A is brought near to Object B, the electrons in Object B travel to the surface which is nearest to Object A.

4. The leaves of a positively charged electroscope are separated. If a physics student, standing on the ground, touches the electroscope with a plastic baseball bat, then the electroscope will be discharged and the leaves will relax to their original rest position.

5. The leaves of a positively charged electroscope are separated. When the electroscope is touched by a person standing upon the ground, the positive charges within the electroscope will be transmitted through the person and into the earth.

Part 5: Short Answer

Using three complete sentences or less, answer three of the following questions.

1. Distinguish between a conductor and an insulator.

2. Distinguish between a positively charged object and a negatively charged object.

3. Distinguish between charging by contact and charging by conduction.

4. Explain how an electrically neutral object can be attracted to a charged body.

5. How can you charge an object negatively with only the help of a positively charged object?

 

 

ELECTROSTATIC   Quiz#2

1. In a neutral atom the number of electrons is equal to

f.        the number of protons.

g.       the number of neutrons.

h.       the sum of the number of protons and neutrons.

i.         the difference between the number of protons and neutrons.

j.         the product of the number of protons and neutrons.

2. An uncharged body would acquire a negative charge if it

d.       gained some atoms.

e.       lost some neutrons.

f.        gained some electrons.

g.       lost some electrons.

h.       gained some protons.

3. A positively charged body must have

d.       an excess of neutrons.

e.       an excess of electrons.

f.        a deficiency of protons.

g.       a deficiency of electrons.

4. A positively charged balloon will be attracted to an electrically neutral wooden cabinet. The explanation of why this occurs is that

d.       the molecules of the wooden cabinet are able to polarize and be attracted to the balloon.

e.       the molecules of the balloon are able to polarize and thus be attracted to the cabinet.

f.        the balloon is a conductor and the wood is an insulator; opposites attract.

g.       the balloon is an insultor and the wood is a conductor; opposites attract.

5. A plastic tube is charged by rubbing it with fur. The plastic tude acquires a negative charge. This is evidence that

f.        plastic molecules have a greater attraction for electrons than fur molecules.

g.       fur molecules have a greater attraction for electrons than plastic molecules.

h.       plastic is an insulator and fur is a conductor.

i.         fur is a insulator and plastic is a conductor.

6. A neutral electroscope is charged by contact using a positively charged electrophorus plate. The electroscope

e.       acquires a positive charge

f.        acquires a negative charge

g.       will merely have a temporary separation of postive and negative charge.

7. A physics student, standing on the ground, touches a plastic baseball bat to a negatively charged electroscope. This will cause

d.       the electroscope to be grounded as electrons flow out of the electroscope.

e.       the needle of the electroscope to deflect even more.

f.        the baseball bat to acquire an excess of protons.

g.       ... absolutely nothing to happen.

8. A negatively charged plastic tube is used to charge a metal sphere by the process of induction. The charge on the metal sphere will be

f.        positive.

g.       negative.

h.       not enough information to tell.

9. An electroscope has an overall negative charge. Thus, the needle of the electroscope is deflected. A positively charged balloon is held just above the plate of the electroscope (without making contact with it). The needle will

f.        deflect even more.

g.       return to the upright position.

h.       remain in a deflected position since there is no contact between balloon and electroscope.

10. An electroscope has an overall positive charge. Jin Erator touches the metal base of the electroscope and grounds the electroscope. The electroscope is no longer charged after the grounding process because

d.       protons flowed through Jin's body into the ground.

e.       electrons flowed through Jin's body into the ground.

f.        electrons flowed throuch Jin's body into the electroscope.

g.       Jin must have been negatively charged prior to touching the electroscope.

11. The needle of a positively charged electroscope will deflect even more when a charged object is brought near the plate of the electroscope. The object MUST be

a.       a conductor.

b.       an insulator.

c.       positively charged.

d.       negatively charged.

e.       neutral.

12. A plastic comb is used to comb a student's hair. The comb is then brought near a negatively charged metal electroscope. If the needle of the electroscope deflects further, the comb has

a.       an excess of electrons.

b.       an excess of protons.

c.       an excess of neutrons.

d.       a deficiency of neutrons.

e.       equal numbers of electrons and protons.

13. The electric force between two charged spheres is 18 units. If the distance between the centers of the spheres is tripled, the resulting electric force will be

a.       6 units.

b.       2 units.

c.       3 units.

d.       54 units.

14. A metal sphere has a deficit of 1.0 x 1012 electrons (charge on 1 electron = 1.6 x 10-19 C). What is the charge on the sphere?

a.       6.25 x 1030 C

b.       1.6 x 10-7 C

c.       -1.6 x 10-7 C

d.       1.6 x 10-31 C

e.       -1.6 x 10-31 C

15. The force of attraction between two point charges can be doubled by

a.       halving the distance between them.

b.       doubling the distance between them.

c.       doubling the charge on both objects.

d.       doubling the charge on one object, only.

 

16. Two oppositely charged balloons with a charge of +5.0 x 10-6 C and -4.0 x 10-7 C experience an electric attractive force with a magnitude of .072 N. Determine the distance between the centers of the two balloons.

 

 

ELECTRIC CURRENT

Quiz #1

Equations:


Part 1: Multiple Choice

 

 

1. Electrons are able to move in an electrical circuit because.

k.       they are continually colliding with other electrons

l.         they are continually colliding with atoms of the conducting wires

m.      an electric potential difference is established across the ends of the circuit

n.       the wires which make up the circuit are so thin

o.       none of the above

2. The role of the power supply in an electric circuit is to

i.         maintain an electric potential difference between the two ends of the circuit.

j.         act as a charge pump in order to pump charge from the - terminal to the + terminal.

k.       do work upon the charge in order to move it from a location of low potential to high potential.

l.         all of the above

m.      none of the above

The circuit at the right shows a lamp bulb connected to a 12-Volt battery. An experimenter measures 3.0 Coulombs of charge flowing out of the battery at location A every 2.0 seconds. Use this information to answer the next four questions.

3. The current in this circuit is

h.       1.5 amps

i.         3.0 amps

j.         6.0 amps

k.       18.0 amps

l.         72.0 amps

4. The amount of charge which flows into the battery at location B is

h.       1.5 C every 2 sec

i.         3.0 C every 1 sec

j.         3.0 C every 2 sec

k.       4.0 C every 2 sec

l.         Not enough information to tell

 

5. The power delivered to the light bulb is.

j.         2.0 Watts

k.       8.0 Watts

l.         12.0 Watts

m.      18.0 Watts

n.       36.0 Watts

6. The amount of work done by the battery to move 3.0 Coulombs of charge from terminal B to terminal A is

h.       4.0 Joules

i.         8.0 Joules

j.         12.0 Joules

k.       18.0 Joules

l.         36.0 Joules

7. A 60 Watt light bulb is connected to a 120 volt plug. What is the current in the light bulb?

h.       0.25 A

i.         0.5 A

j.         2 A

k.       4 A

l.         more than 4 A

 

 

 

8. The current flow in a conducting wire will _________ as the length of that wire is increased.

i.         increase

j.         decrease

k.       remain the same

9. Which one of the following does not represent units of current?

i.         amperes

j.         volt/ohm

k.       C/sec

l.         J/C

10. A kilowatt x hour is a unit of

h.       potential

i.         force

j.         current

k.       energy

l.         power

11. A device used to measure current is known as the ___________.

f.        voltmeter

g.       ammeter

h.       watthour meter

i.         potentiometer


12. Which one of the following symbols represents the schematic circuit symbol of a resistor?

 

13. A circuit consists of a 6-Volt battery and a lamp bulb. The battery does 12 J of work in order to move 2 C of charge through the internal circuit. As the 2 C charge flows through the external circuit, it does _______ of work upon the light bulb.

f.        1 J

g.       2 J

h.       6 J

i.         12 J

j.         24 J

14. Charge encounters resistance as it flows through circuits because of

e.       collisions with atoms in the conducting elements.

f.        the presence of insulators within the conducting elements.

g.       the rate at which a battery does work is less than the rate at which charge is able to flow.

h.       the inability of humans to produce the extreme voltages required for reducing resistance.


A power supply, light bulb, and two ammeters are connected in a circuit as shown below. Use the information in the diagram to answer the following questions.

15. The ammeter at the "bottom" of the diagram will read

f.        more than 0.5 amps

g.       0.5 amps

h.       less than 0.5 amps

i.         not enough information to tell

16. The voltage of the power supply is

e.       0.5 Volts

f.        3 Volts

g.       6 Volts

h.       12 Volts

17. Conventional current will flow through the external circuit from

a.       B to D to C to A

b.       A to C to D to B

c.       A to B

d.       B to A

18. The electric potential at A is ____________ the electrical potential at C.

a.       less than

b.       greater than

c.       approximately equal to

19. The electric potential at C is ____________ the electrical potential at D.

a.       less than

b.       greater than

c.       approximately equal to

20. The amount of energy lost by 1 Coulomb of charge as it flows through the external circuit is

a.       0.5 Joules

b.       3 Joules

c.       6 Joules

d.       12 Joules


Anna Litical performed an experiment to measure the resistance of three different electrical devices (A, B, and C). Anna set up a circuit and collected voltage-current data for each of the three devices. Anna then constructed graphs of Voltage vs. Current for her data. Her data sets are shown below. Use the data in the tables to answer the next several questions.

 

21. An analysis of Anna's data would indicate that the device with the greatest resistance is

a.       Device A

b.       Device B

c.       Device C

d.       Not enough info to tell

22. The device which fails to obey Ohm's law seems to be

a.       Device A

b.       Device B

c.       Device C

d.       Not enough info to tell

23. An analysis of the data set for Device C show that one of the pairs of measured data (0.25 V, 0.79 amps) seems to be inconsistent with the other measurements. The best way for Anna to treat this particular data pair is

a.       to change the current measurement to a more consistent value, such as 0.50 amps.

b.       to conclude that the device acts inconsistent at a voltage of 0.25 V.

c.       to repeat the measurement of voltage for a current of 0.79 amps (assuming time permits).

d.       to repeat the measurement of current at the voltage of 0.25 V (assuming time permits).

24. An analysis of the data set for Device A shows that the ratio of V/I for each data pair is not exactly constant. The appropriate response to this fact would be to

a.       change certain measured values until the ratio of V/I is constant.

b.       conclude that the V/I ratio should not be constant.

c.       discard the data and repeat the experiment until the ratio of V/I is constant.

d.       blame the lack of a constant V/I ratio upon faulty equipment.

e.       construct a graph

25. A voltage vs. current graph of the data for Device A would look like the graph at the right.  If the axes were reversed and a graph of current vs. voltage was constructed instead, then the graph would look like. 

 


 

 

 

 

Part 2: Problem-Solving

 

For the following problems, show all your work (with units) to receive full or partial credit. The solution to each problem will demand a careful treatment of units, thoughtful reasoning, and the appropriate usage of more than one equation.

 

 

 

26. An electric heater provides 2.00 kW of power when connected to a 120-V potential difference. How much energy is used if the heater is on for five hours?

 

 

 

27. Eighty percent of the electrical energy used by a sun lamp is converted into thermal energy. When the sun lamp is plugged into a 120-V outlet, it draws 2.00 A. How much thermal energy (heat) is released by this lamp in 30.0 minutes?

ELECTRIC CURRENT

Quiz#2

Equations:

 

 

 

 

Part 1: Multiple Choice

1. A 100-W and a 60-W light bulb is used in two different lamps in your home. The difference between a 100-W light bulb and a 60-W light bulb is the

p.       voltage drop across the 100-W light bulb is greater than that of the 60-W light bulb.

q.       current flowing through the 60-W light bulb is greater than that of the 100-W light bulb.

r.        the resistance of the 60-W light bulb is greater than that of the 100-W light bulb.

s.       the energy delivered to the 60-W light bulb is greater than that of the 100-W light bulb.

t.        two of the above.

2. A 3-Volt battery, a resistor, and an ammeter are connected in series in a circuit. If the 3-Volt battery is replaced by a 6-Volt battery, then

n.       the resistance of the resistor will decrease by a factor of two.

o.       the resistance of the resistor will increase by a factor of two.

p.       the ammeter reading will decrease by a factor of two.

q.       the ammeter reading will increase by a factor of two.

r.        None of the above; both the current and the resistance will remain constant.

3. Where do the electrons which flow through the circuit to light your household lamps originate?

m.      The electrons originate at the power plant and travel to our homes through power lines.

n.       The electrons originate in the fuse box of the home.

o.       The electrons were present in the wires of the circuit before the switch was "flipped."

p.       The electrons originate in the switch; when flipped, they flow from the switch to the lamp.

q.       Nonsense ... electrons do not move through the wires; only positive charge flows.

4. The speed at which charge flows through electrical circuits is

m.      very small because moving charge is continually colliding with atoms.

n.       very large because the strength of the electric field exerts large forces upon moving charge.

o.       not possible to determine because lights turn on immediately after the switch is "flipped".

p.       sometimes very large and sometimes very small, depending upon the age of the battery.

5. Increasing the current in a resistor by a factor of five will increase the heat produced by the resistor by a factor of

o.       1/5

p.       1/25

q.       5

r.        25

6. The resistance in a conducting wire will ___________ as the diameter of that wire is increased.

m.      increase

n.       decrease

o.       remain the same

7. The resistance in a conducting wire will ____________ as the length of that wire is increased.

m.      increase

n.       decrease

o.       remain the same

8. Which one of the following factors would not allow for the transmission of electric energy over long distances with very little energy losses?

l.         The use of wires with low resistance.

m.      The use of high voltage power lines.

n.       The use of a high current.

9. The power loss of a resistor is equal to _____________.

m.      IR2

n.       I/V

o.       I2R

p.       I2 Rt

10. The work required to move 2 coulombs of charge through a potential difference of 5 volts is

m.      10 joules

n.       2 joules

o.       25 joules

p.       50 joules.

11. How many coulombs of charge move past point "x" in 10 seconds? (See diagram below)

j.         0.50

k.       5.0

l.         12

m.     

48

 

 

12. Current is a measure of

k.       the force that moves a charge past a point.

l.         the resistance to the movement of charge past a point.

m.      the energy used to move a charge past a point.

n.       the amount of charge that moves in a certain time past a point.

o.       the speed that the charge moves past a point.

13. One volt is equivalent to

i.         1 W-s

j.         1 J/s

k.       1 J/C

l.         1 s/J.

m.      1 C/J.

14. A current of 0.80 A flows for 1.0 min. The total electric charge passing a point in this time is

j.         0.80 C.

k.       1.3 C.

l.         48 C.

m.      75 C

n.       2.9 x 103 C.

15. How much chemical energy will the battery convert to electrical energy in 10 seconds? See diagram at right.

i.         24 joules

j.         240 joules

k.       360 joules

l.         600 joules

 


16. A resistor is placed in a circuit with a power supply. A student wishes to measure the current throught the resistor and the voltage drop across the resistor. Which circuit in the diagram below shows the meter(s) connected correctly?

 

 

 

 

 

 

 

 

 

Use the circuit diagram at the right to answer the next two questions.

17. The electric current through the light bulb is

e.       0.67 ampere

f.        2.0 amperes

g.       6.0 amperes

h.       4.0 amperes

18. The resistance of the light bulb is

d.       1.0 ohm

e.       0.5 ohm

f.        0.17 ohm

g.       23.5 ohms

 

 

 

Use the circuit diagram below to answer the next three questions.

 

19. The potential difference between X and Y is

d.       24 V

e.       16 V

f.        12 V

g.       8.0 V

h.       2.0 V

 

20. The equivalent resistance of the circuit is

e.       24 ohm

f.        6.0 ohm

g.       2.0 ohm

h.       1.3 ohm

i.         0.75 ohm

21. The current at Y is

e.       2.0 A.

f.        2.7 A.

g.       4.0 A.

h.       6.0 A.

i.         1.4 x 103 A.

22. Two 10 ohm resistors connected IN SERIES draw a larger current from a battery than a single 10 ohm resistor would draw.

e.       True

f.        False

23. As resistors are added in parallel to a circuit, the current in the circuit

e.       decreases

f.        increases

g.       remains the same.

24. A 12 ohm resistor is connected in parallel with a 6.0 ohm resistor. The equivalent resistance is

f.        18 ohm

g.       12 ohm

h.       6.0 ohm

i.         4.0 ohm

j.         0.25 ohm

Use the diagram at the right to answer the next three questions.

25. The potential difference across the ends of resistor R2 is

a.       0.67 volt

b.       1.5 volts

c.       6.0 volts

d.       28 volts

26. Compared to the potential difference across R2, the potential difference across R1 is

a.       one-half as great.

b.       twice as great.

c.       the same.

d.       four times as great.

 

27. Compared to the rate of heat production in R2, the rate of heat production in R3 is

a.       less

b.       greater

c.       the same.

28. In the diagram at the right, ammeter A reads 5 amperes and ammeter B reads 2 amperes, as shown. The reading of ammeter C is

a.       1.4 amp

b.       5 amp.

c.       3 amp

d.       7 amp.

29. How much energy is consumed when a 60.0 W light bulb is left on for 3.00 h?

a.       20.0 J

b.       180 J

c.       540 J

d.       10.8 kJ

e.       648 kJ

 

30. How long must a 100-watt light bulb be used in order to dissipate 1,000 joules of electrical energy?

a.       10 sec

b.       100 sec

c.       1,000 sec

d.       100,000 sec.

Part 2: Short Answer

31. Using conversion factors, convert the quantity 1 kiloWatt x hour to units of Joules. Show all your conversion factors in the space below.


32. The table below lists quantities discussed in the last two units. For each quantity, list the symbol used to represent that quantity and write the full name of the standard metric unit for that quantity.

 


Four resistors (A, B, C, and D) are placed in a circuit and connected to a 24-V power supply. Two of the resistors and connected in parallel and two of the resistors are connected in series. Ammeters are placed in the circuit to measure the current passing through each resistor. The measured currents and the known resistances of the four devices are shown below. Use this information to answer the next three questions.

 

33. Which two resistors are placed in series? ___________ in parallel? ___________

34. Construct a circuit diagram of this circuit. Use the appropriate circuit symbols. Label each resistor as A, B, C, and D. Be sure to show the placement of the ammeters in the circuit. Indicate the voltage of the power supply.

35. Fill in the remaining column of the data table above, showing the voltage drop across each resistor.

 

MAGNETISM

 

http://www.mcwdn.org/Physics/MagnetQuiz.html

 

1. This is a force where objects are attracted or repelled to one another:

a)light

b) sound

c) magnetism

 

2. Magnets have a north seeking pole and a south seeking pole.

a) True

b) False

3. Two of the same kinds of poles repel each other.

a) True

b) False

4. Two opposite poles attract each other.

a) True

b) False

5. The area around a magnet that behaves like a magnet is a magnetic

a) color

b) field

c) sound

6. The further apart two magnets are from one another the stronger the forces that attract or repel the magnets.

a) True

b) False

7. When magnets are broken into small bits, the bits themselves can become small magnets.

a) True

b) False

8. Naturally occurring magnets in nature are called

a) plastic

b) stones

c) lodestones

9. Which of these is not used to create a simple electromagnet?

a) battery

b) bulb

c) copper wire