                8.3 Practicals & Worksheets    ELECTRICAL ENERGY WORKSHEETS

# ELECTROSTATICS WORKSHEET No.1

This worksheet is designed to assist you in making a brief summary of some important electrostatic concepts.

1. Discuss whether the different views held by Galvani and Volta on the nature of electricity contributed to an increased understanding of electricity.

2. Define the term “electrostatics”.

3. State the rules regarding charge discovered by Gilbert, Franklin and other scientists.

4. State Coulomb’s Law in words and give the equation that expresses this statement mathematically.  Make sure to define all the symbols used.

5. State the SI units of charge.  Give the name of the unit and the symbol.

6. Define the concept of an “electric field”.  Give a mathematical definition for the strength of such a field.  Define all terms used and state the SI units of electric field strength.

7. Explain how the direction of an electric field is determined.

8. Explain how “lines of force” can be used to represent electric fields diagrammatically.

9. Draw the electric field present in each of the following situations:
1. Around isolated point charges
2. Around a dipole
3. Between two parallel charged plates

10. If a positive and a negative charge of equal size, 5 x 10-6 C, were located 2 x 10-8 m apart in a vacuum (as shown in diagram (b) above), determine the size of the force acting on each charge.  (Force is measured in newtons, symbol N.)  (Answer: 5.625 x 1014 N)

11. Would the force in (11) be attractive or repulsive for the two charges involved?

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# ELECTROSTATICS WORKSHEET No.2    2. Answer all of the following questions:

¨      Explain in words what you understand the term “electric field” to mean and give a mathematical definition of the strength of such a field.

¨      A charge of 5C experiences a force of 100N due west when placed into a uniform electric field.  Determine the size and direction of the field.

¨      Calculate the size of the force that would be experienced by a 3mC charge placed into a uniform electric field of strength 1 x 105 NC-1.

¨      A  - 5mC charge travels due south under the influence of a 10N force when placed into a uniform electric field.  What force would a 10mC charge experience if placed in the same field and in which direction would it move?

¨      State in words the definition of the potential difference between two points in an electric field.

¨      A charge of 15mC experiences a gain in potential energy of 60J in moving from point X to point Y in a uniform electric field.  Determine the potential difference between points X and Y.

¨      On an electrostatic surface, such as the surface of a Van de Graaff generator, no work is needed to move charge from one point to another on the surface.  What does this tell you about the potential difference between points on such a surface?

# ELECTRIC CIRCUIT WORKSHEET NO.1

NOTE: While thinking and talking about the following questions practise using the language of Physics correctly.  Current is a flow of charge, so it is correct to talk about the “current flowing through a resistor”.  Potential difference or voltage exists between two points in a circuit, so we speak of “the potential difference across a resistor” or “the voltage drop across a resistor”.  DO NOT say things like, “the voltage flowing through the resistor” etc!!!  Voltage does not flow anywhere, so don’t say it!!!  You can speak about the voltage or potential “at a particular point in a circuit”.  For instance, you might say, “the voltage at the positive terminal of a 12 V battery is 12 V”.  Good communication is essential in all sciences.  So, use the language correctly.

1.      A circuit consists of a 12 V battery connected across a single resistor.  If the current in the circuit is 3 A, calculate the size of the resistor.  (4W)

2.      Two 5W resistors are connected in series with a 12 V battery.  Determine: (a) the potential difference across each resistor; and (b) the current flowing in the circuit. (6 V, 1.2 A)

3.      Two resistors of size 10W and 5W are connected in parallel as shown below. a.      If 3.6 A of current flows into the parallel branch, determine the current flowing in each of the resistors.  (2.4 A in the top resistor & 1.2 A in the bottom resistor)

b.      What is the potential difference across each of the resistors?  (12V)

c.       How much current will flow out of the parallel branch?  (3.6 A)

4.      Consider the following circuit and then answer the questions below. a.      State the potential difference between X and Z.

b.      State the potential difference between X and Y.

c.       How much potential is left at Y?

(Answers: (a) 12V, (b) 8V, (c) 4V)

5.      The circuit below shows a resistor, R, connected in series to a 12 V battery across an open switch, S. a.      If R = 6W, how much current flows in the circuit with the switch open?

b.      While the switch remains open, determine the potential difference between:

i.      A and B

ii.      A and C

iii.      B and C

c.       When the switch is closed and R = 6W, determine:

i.      the current in the circuit;

ii.      the potential difference between A and B; and

iii.      the potential difference between B and C.

(b)(i) 12V, (ii) 12V, (iii) 0V

(c)(i) 2A, (ii) 0V, (iii) 12V

# ELECTRIC CIRCUIT WORKSHEET NO.2

1.      Find the current in the 20W and 5W resistors in the following circuit. (Answers: I20 = 0.045 A and I5 = 0.18 A)

2.      In the circuit below, the reading on the ammeter is 3.2 A. Determine:

a.      the reading on the voltmeter;

b.      the potential difference across the 40W resistor; and

c.       the current in the 40W resistor.

(Answers: (a) 32V, (b) 18V, (c) 0.45A)

3. For the circuit above:

a.      Determine the total resistance.

b.      Find the reading on the ammeter.

c.       Draw a voltmeter in the correct place to measure the potential difference across the 0.3W resistor.

d.      Draw an ammeter in the correct place to measure the current in the 0.3W resistor.

e.      Determine the readings on the meters mentioned in parts (c) and (d) above.

W, (b) 0.2A, (c) voltmeter in parallel across the resistor, (d) ammeter in series with the resistor, (e) ammeter reading = 0.125A and voltmeter reading = 0.0375V)

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# ENERGY & POWER WORKSHEET NO.1

Answers are supplied.  Simply click on the word "answers" at the end of each question.

1.      Consider the circuit below, which shows four identical lamps A, B, C and D in a circuit, controlled by switches S1, S2 and S3. a.      Which globes would light when the following occurs:

i.      S1 only is closed;

ii.      S1 and S2 are closed;

iii.      S1 and S3 are closed;

iv.      all three switches are closed?

b.      When all switches are closed, globes A and B do not glow as brightly as globe D.  Explain why this is so.

c.       Comment on the brightness of globe C compared with globe D, when all switches are closed.

2.      An electric radiator uses a voltage of 240 V and draws a current of 2 A for a total time of 3 hours.  Calculate the total energy dissipated by the radiator.  Answers

3.      The electrical energy used in one hour by a tungsten filament light globe is 1.44 x 105 J.  If the current flowing through the tungsten filament is 0.17 A, calculate the resistance of the tungsten filament.  Answers

4.      Consider the circuit shown below. The reading on the ammeter is 0.9 A and that on the voltmeter is 3.36 V.  Determine the power dissipated by the:

a.      whole circuit;

b.      5W resistor;

c.       10W resistor.

5.      Consider the circuit shown below.  The G in the circle represents a galvanometer, which is a very sensitive current measuring device.  The galvanometer is connected between points X and Y in the circuit. For this circuit:

a.      determine the total resistance;

b.      calculate the current in each parallel arm;

c.       find the potential difference across the 1W resistor;

d.      find the potential difference across the 2W resistor;

e.      determine the potential difference between X and Y;

f.        state the reading on the galvanometer;

g.      calculate the power dissipated by this circuit.

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# ANSWERS TO ENERGY & POWER WORKSHEET NO.1

1.      (a) (i) None – no closed circuit; (ii) A, B, D glow; (iii) D, C glow; (iv) all globes

(b) Current in D is higher than in A & B, since A & B are in one of the two parallel arms of the circuit.  Power is proportional to the square of the current.  So, power in D > power in A & B and therefore globe D glows more brightly.

(c) Globe C will be less bright.  Lower current and therefore lower power and brightness.

2.      5.2 x 106 J

3.      1384 W

4.      (a) 13.5W; (b) 4.05 W; (c) 1.13 W

5.      (a) 3.33W; (b) current in top arm = 2A, current in bottom arm = 1A; (c) 2V;

(d) 2V; (e) 0V; (f) 0A; (g) 30W

# OHM’S LAW PRACTICAL

AIMS:

1.      To gain practical experience in setting up electrical circuits and using ammeters, voltmeters and variable resistors (rheostats).

2.      To demonstrate Ohm’s Law.

METHOD:

1.      Set up the following circuit.  Note that the rheostat used has a 6.5A, 10W rating. 2.      By varying the resistance of the rheostat, adjust the current in the circuit to the values shown in Table No.1 below.  For each value of total current in the circuit, record the potential difference across the 2W resistor.

3.      On the graph sheet provided, draw a graph of potential difference versus current and show the calculation of the slope of the graph.

RESULTS:

1.
TABLE No.1: Potential Difference and Current Values

 Potential Difference (V) Current (A) 0.5 1.0 1.2 1.5 2.0

2.      What does the shape of your graph tell you about the relationship between the potential difference across the fixed resistor and the current flowing through the fixed resistor?

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3.      Slope of graph (including units) =

4.      Compare the value of your slope with the known value of the fixed resistor used in this experiment.

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5.      Justify the placement of the ammeter and voltmeter in the circuit used for this experiment.

Ammeter: _______________________________________________

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Voltmeter: _______________________________________________

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# POWER OF A HEATING COIL PRACTICAL

AIMS:

1.      To gain practical experience in setting up electrical circuits and using ammeters and voltmeters.

2.      To demonstrate the relationship between current, voltage and power for a model 6V to 12V electric heating coil.

METHOD:

1.      Set up the following circuit.  Use a standard 0-12V power pack as your voltage source.  Note that a 2W resistor is being used as the heating coil.  If we so desired, we could also immerse the 2W resistor (properly enclosed) in a water bath to reduce the risk of burning it out.  The extra 2W resistor is used to keep the current to a reasonable level. 2.      For each value of “voltage supplied by the power supply” shown in Table No.1 in the Results section, record the current in the circuit and the voltage drop across the heating coil.

3.      Complete the table by filling in the resistance and power values for the heating coil for each voltage setting.  Show a sample calculation for each physical quantity in the space provided in the Results section.

4.      Supply the correct units for the resistance and power columns in the table.

RESULTS:

1.      TABLE No.1: Power Values for Heating Coil

 Voltage Supplied by Power Supply (V) Voltage Drop Across Coil (V) Current (A) Resistance   Units = Power   Units = 2 4 6 8

2.      Sample Calculations – When “Voltage Supplied by Power Supply” = 2V:

Resistance of heating coil

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Power dissipated by heating coil

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3.      Summary: State the relationship between current, voltage and power in electric circuits.

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# ASSORTED ELECTRICAL PRACTICALS

Click on this link to access this pdf file.

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# COMMENT ON LABORATORIES

There are many good laboratories that can be done in the "Electrical Energy in the Home" topic.  I will continue to publish others on this site as I get time.

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