Web viewIB Electricity WS 01 Qs. 1. This question is about electric circuits. (a)(i)Define emf and...

IB Electricity WS 01 Qs

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IB Electricity WS 01 Qs of 23

IB Electricity WS 01 Qs

1. This question is about electric circuits.

(a) (i) Define emf and state Ohm’s law.

emf: ....................................................................................................

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Ohm’s law: ....................................................................................................

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(ii) The graph below shows the I-V characteristic of a particular electrical component.

0 0

V

I

State show the resistance of the component is determined from the graph.

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(b) In the circuit below an electrical device (load) is connected in series with a cell of emf 2.5 V and internal resistance r. The current I in the circuit is 0.10 A.

lo ad

I = 0 .1 0 A

e .m .f. = 2 .5 V

r

The power dissipated in the load is 0.23 W.

Calculate

(i) the total power of the cell;

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(ii) the resistance of the load;

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(iii) the internal resistance r of the cell.

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(c) A second identical cell is connected into the circuit in (b) as shown below.


lo ad

I = 0 .1 5 A

The current in this circuit is 0.15 A. Deduce that the load is a non-ohmic device.

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(Total 12 marks)

2. This question is about electric circuits.

(a) Define emf and state Ohm’s law.

emf: .............................................................................................................

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Ohm’s law: .............................................................................................................

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(b) In the circuit below an electrical device (load) is connected in series with a cell of emf 2.5 V and internal resistance r. The current I in the circuit is 0.10 A.

lo ad

I = 0 .1 0 A

e .m .f. = 2 .5 V

r

The power dissipated in the load is 0.23 W.

Calculate

(i) the total power of the cell;

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(ii) the resistance of the load;

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(iii) the internal resistance r of the cell.

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(c) A second identical cell is connected into the circuit in (b) as shown below.

lo ad

I = 0 .1 5 A

The current in this circuit is 0.15 A. Deduce that the load is a non-ohmic device.

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(Total 11 marks)

3. This question is about electrical resistance.

(a) Define electrical resistance.

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(b) (i) Three resistors, each of resistance 6.0 , are connected as shown below.

6 .0 A

B

6 .0 6 .0

Calculate the total resistance between point A and point B of this arrangement.

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(ii) The arrangement in (b)(i) is now connected to two more resistors, as shown below. Each resistor is of resistance 6.0 .

6 .0

6 .0 6 .0 6 .0

6 .0 A

B

C

D

Using your answer in (b)(i), deduce that the total resistance between point C and point D is 8.4 .

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(iii) One of the resistors in the arrangement shown in (b)(ii) becomes faulty. The resistance between point C and point D is found to be 6.0 . On the diagram in (b)(ii) above, identify the faulty resistor by drawing a circle around it. Deduce the nature of the fault.

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(Total 6 marks)

4. This question is about electrical circuits.

The graph below shows the I-V (current-voltage) characteristic of an electrical component T.

1 5 0

1 0 0

5 0

00 .0 2 .0 4 .0 6 .0 8 .0

I / m A

V / V

(a) On the graph above, draw the I-V characteristic in the range V = 0 to V = 6.0V for a resistor R having a constant resistance of 40.

(1)


(b) The component T and the resistor R are connected in parallel as shown below.

T

R

A B

4 0

When a battery of constant emf E and negligible internal resistance is connected between the terminals A and B, the current in the resistor R is 100 mA.

(i) Calculate the emf E of the battery.

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(ii) Use the graph to determine the current in T.

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(iii) Calculate the power dissipation in T.

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(c) In order to reduce the power dissipation in component T, a second resistor R of resistance 40 is connected in series with T. The circuit is shown below.

T R

A

R

B

4 0

The battery connected between A and B is unchanged.

Use the graph to determine

(i) the current in resistor T.

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(ii) the power dissipation in T.

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(Total 9 marks)


5. This question is about an electric circuit.

A particular filament lamp is rated at 12 V, 6.0 mA. It just lights when the potential difference across the filament is 6.0 V.

A student sets up an electric circuit to measure the I-V characteristic of the filament lamp.

In the circuit, shown below, the student has connected the voltmeter and the ammeter into the circuit incorrectly.

The battery has emf 12 V and negligible internal resistance. The ammeter has negligible resistance and the resistance of the voltmeter is 100 k. The maximum resistance of the variable resistor is 15.

(a) Explain, without doing any calculations, whether there is a position of the slide S at which the lamp will be lit.

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(b) Estimate the maximum reading of the ammeter.

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(c) Complete the circuit diagram below showing the correct position of the voltmeter and of the ammeter in order to determine the I-V characteristic of the filament lamp.

(2)(Total 7 marks)

6. This question compares the electrical properties of two 12 V filament lamps.

A lamp is designed to operate at normal brightness with a potential difference of 12 V across its filament. The current in the filament is 0.50 A.

(a) For the lamp at normal brightness, calculate

(i) the power dissipated in the filament.

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(ii) the resistance of the filament.

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In order to measure the voltage-current (V-I) characteristics of a lamp, a student sets up the following electrical circuit.

1 2 V b a tte ry

(b) On the circuit above, add circuit symbols showing the correct positions of an ideal ammeter and an ideal voltmeter that would allow the V-I characteristics of this lamp to be measured.

(2)

The voltmeter and the ammeter are connected correctly in the previous circuit.

(c) Explain why the potential difference across the lamp

(i) cannot be increased to 12 V.

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(ii) cannot be reduced to zero.

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An alternative circuit for measuring the V-I characteristic uses a potential divider.

(d) (i) Draw a circuit that uses a potential divider to enable the V-I characteristics of the filament to be found.

(3)

(ii) Explain why this circuit enables the potential difference across the lamp to be reduced to zero volts.

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The graph below shows the V-I characteristic for two 12 V filament lamps A and B.

1 2

00 0 .5 1 .0

cu rren t / A

P o ten tia ld iffe ren ce/ V

lam p A lam p B

(e) (i) Explain why these lamps do not obey Ohm’s law.

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(ii) State and explain which lamp has the greater power dissipation for a potential difference of 12 V.

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The two lamps are now connected in series with a 12 V battery as shown below.

lam p A lam p B

1 2 V b a tte ry

(f) (i) State how the current in lamp A compares with that in lamp B.

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(ii) Use the V-I characteristics of the lamps to deduce the total current from the battery.

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(iii) Compare the power dissipated by the two lamps.

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(Total 25 marks)


7. This question is about emf and internal resistance.

A dry cell has an emf E and internal resistance r and is connected to an external circuit. There is a current I in the circuit when the potential difference across the terminals of the cell is V.

V

r

EI

(a) State expressions, in terms of E, V, r and I where appropriate, for

(i) the total power supplied by the cell;

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(ii) the power dissipated in the cell;

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(iii) the power dissipated in the external circuit.

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(b) Use your answers to (a) to derive a relationship between V, E, I and r.

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The graph below shows the variation of V with I for the dry cell.

1 .6

1 .5

1 .4

1 .3

1 .2

1 .1

1 .0

0 .9 0

0 .8 0

0 .7 0

0 .6 0

0 .5 0

0 .4 0

0 .3 0

0 .2 0

0 .1 0

0 .0

V / V

0 .0 0 .1 0 0 .2 0 0 .3 0 0 .4 0 0 .5 0 0 .6 0 0 .7 0 0 .8 0 0 .9 0 1 .0 1 .1 1 .2 1 .3

I / A


(c) Complete the diagram below to show the circuit that could be used to obtain the data from which the graph was plotted.

(3)

(d) Use the graph, explaining your answers, to

(i) determine the emf E of the cell;

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(ii) determine the current in the external circuit when the resistance R of the external circuit is very small;

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(iii) deduce that the internal resistance r of the cell is about 1.2 Ω.

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(e) The maximum power dissipated in the external circuit occurs when the resistance of the external circuit has the same value as the internal resistance of the cell. Calculate the maximum power dissipation in the external circuit.

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(Total 18 marks)

8. This question is about modelling the thermal processes involved when a person is running.

When running, a person generates thermal energy but maintains approximately constant temperature.

(a) Explain what thermal energy and temperature mean. Distinguish between the two concepts.

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The following simple model may be used to estimate the rise in temperature of a runner assuming no thermal energy is lost.

A closed container holds 70 kg of water, representing the mass of the runner. The water is heated at a rate of 1200 W for 30 minutes. This represents the energy generation in the runner.

(b) (i) Show that the thermal energy generated by the heater is 2.2 × 106 J.

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(ii) Calculate the temperature rise of the water, assuming no energy losses from the water. The specific heat capacity of water is 4200 J kg−1 K−1.

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(c) The temperature rise calculated in (b) would be dangerous for the runner. Outline three mechanisms, other than evaporation, by which the container in the model would transfer energy to its surroundings.

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A further process by which energy is lost from the runner is the evaporation of sweat.


(d) (i) Describe, in terms of molecular behaviour, why evaporation causes cooling.

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(ii) Percentage of generated energy lost by sweating: 50%Specific latent heat of vaporization of sweat: 2.26 × 106 J kg−1

Using the information above, and your answer to (b) (i), estimate the mass of sweat evaporated from the runner.

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(iii) State and explain two factors that affect the rate of evaporation of sweat from the skin of the runner.

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(Total 25 marks)


9. This question is about the force between current-carrying wires.

Diagram 1 below shows two long, parallel vertical wires each carrying equal currents in the same direction. The wires pass through a horizontal sheet of card. Diagram 2 shows a plan view of the wires looking down onto the card.

sh ee t o f ca rd

ey e

d ia g ram 1 d ia g ram 2

(a) (i) Draw on diagram 1 the direction of the force acting on each wire.(1)

(ii) Draw on diagram 2 the magnetic field pattern due to the currents in the wire.(3)

(b) The card is removed and one of the two wires is free to move. Describe and explain the changes in the velocity and in acceleration of the moveable wire.

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(Total 7 marks)


Web viewIB Electricity WS 01 Qs. 1. This question is about electric circuits. (a)(i)Define emf and...

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