As CT - Waves & Electricity - JAN 2012

8/3/2019 As CT - Waves & Electricity - JAN 2012

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MESH INTERNATIONAL WAVES & ELECTRICITY (ALP AS) CT:

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1. (a) Explain why the resistance of a metallic conductor increases when its temperature is increased.

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(b) A lamp filament of length 0.17 m is made from tungsten. The radius of the filament is 2.1 10-5

m

and its resistance is 6.0 . Calculate the resistivity of tungsten.

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2. Figures 2 shows a circuit in which there is a current in a metallic resistor, R, and in a salt solution, S.

Figure 2

The dots in R and S indicate the charge carriers in those materials.

(i) Label on Figure 2 the names and charges of each charge carrier.

(ii) Draw arrows on Figure 2 to show the directions of drift of the charge carriers shown. (5)

3. (a) (i) Describe what is meant by a superconductor.

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(ii) Sketch onto the axes below a graph of the variation of the resistance of a superconductor with

temperature in C. (3)

(b) (i) State a use for superconductors.

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(ii) State an advantage of the use of superconductors compared with the use of ordinary conductors.

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4. One design for a set of coloured warning lights has a single lamp illuminating three different

coloured lenses. It is shown in Figure 4.1.

Figure 4.1

(a) (i) The lamp draws a current of 3.0 A from a 14 V supply that has no internal resistance.

Calculate the power of the lamp.

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(ii) An alternative design has three separate 2.0 A lamps, one illuminating each of the lenses.

The lamps are connected in a parallel combination which is then connected to the same supply as in

part (a)(i). The arrangement is shown in Figure 4.2.

Figure 4.2

Calculate the resistance of each lamp.

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(iii) Calculate the total resistance of the parallel combination of lamps.

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(iv) State the advantage of the parallel combination compared with the single lamp.

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(b) A 4.5 resistor is placed in series with a battery of emf 14 V. The current through the resistor is

2.9 A.

Figure 4.3


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(i) Calculate the internal resistance, r, of the battery.

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(ii) Calculate the voltage lost across the internal resistance.

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5. Figure 5 shows the mode of vibration for a stretched string of length 0.45 m when it is emitting a

note of frequency 900 Hz.

Figure 5

(a) (i) How many nodes are there in the waveform?

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(ii) State the wavelength of the waves shown in Figure 5.

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(b) (i) Calculate the speed of waves along the string.

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(ii) The maximum frequency of vibration of this string that can be heard by an observer is 3600 Hz.

How many loops would occur when the string is emitting this frequency?

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6. The aircraft shown in Figure 6 is flying horizontally at 125 ms-1

. The flight path is directly over two

radio transmitters that are known to be 550 m apart. The transmitters emit coherent waves of

wavelength 32 m. The pilot notices that the signal strength varies and is a minimum every 3.2 s.

Figure 6

(a) Explain what is meant by coherent waves and why the strength of the signal received varies.

Two of the 7 marks are available for the quality of your written communication.

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(b) (i) Calculate the distance travelled by the aircraft between one position of minimum signal

strength and the next.

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(ii) Calculate the height at which the aircraft is flying.

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7. A student is provided with two 1.0 k metal resistors and a negative temperature coefficient

thermistor of initial resistance 1.5 k at 20C.

(a) Calculate the minimum value of resistance that can be produced when using all three components

at 20C. Draw a diagram to make it clear how the components are connected together to achieve this

minimum resistance.

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(b) When charge flows through the resistor network, the temperature of each component rises.

State and explain the changes in resistance that occur in each of the components as a result of the

changes in temperature.

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8. (a) Describe the difference between longitudinal and transverse waves.

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(b) (i) Light from a lamp is unpolarised. Explain how this light is different from light that has been

passed through a polarising filter.

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(ii) Name an example of a wave that cannot be polarised and explain why.

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9. (a) Figure 9.1 shows two loudspeakers emitting identical sound waves of wavelength 0.15m. The

loudspeakers are 1.0 m apart. A regular rise and fall in sound intensity can be detected by an observer

moving from A to B in the area where the two sound waves from the loudspeakers overlap.

Figure 9.1


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Calculate the separation of two adjacent positions of maximum sound intensity in the interference

pattern between A and B.

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(b) Figures 9.2 and 9.3 each show situations in which waves from two sources overlap. In

Figure 9.2, two lamps, emitting white light with a range of wavelengths of 4.5 10-7

m to 7.0 10-7

m,

are separated by 1.0 m. In Figure 9.3, two loudspeakers, connected to the same signal generator, are

separated by 1.0 m. The wavelength of the sound from each speaker is 0.15 m.

Figure 9.2 Figure 9.3

In Figure 9.2 an observer moves between A and B and does not see interference maxima and minima.

In Figure 9.3 an observer moves between A and B and does hear interference maxima and minima.

Explain why interference is detected with the sound (Figure 9.3) but not with the light (Figure 9.2).

Two of the 7 marks are available for the quality of your written communication.

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10. (a) Explain how a standing wave is formed.

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(question continues on next page)


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(b) Figure 10.1 shows a loudspeaker, emitting a sound of single frequency, positioned in front of a

wall. A standing (stationary) wave is produced between the loudspeaker and the wall. A microphone,

connected to an oscilloscope, is used to detect positions of maximum amplitude (labelled M) on the

standing sound wave. Places marked M are antinodes on the standing wave. The microphone and

oscilloscope are not shown on the diagram.

Figure 10.1

Figure 10.2 shows the oscilloscope trace observed when the microphone is in one of the positions

labelled M. Each grid square measures 1cm by 1cm. The time-base of the oscilloscope is set to 2 ms

per division.

Figure 10.2

(i) Use data from Figure 10.2 to show that the frequency of the sound is approximately 630 Hz.....................................................................................................................................................................

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(ii) Use data from Figure 10.2 to find the wavelength of the sound.

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(iii) Calculate the speed of sound in air.

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TOTAL FOR THIS PAPER: 72 MARKS

As CT - Waves & Electricity - JAN 2012

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