# Physics Exam Questions

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Explain how the I-V characteristic shows the resistivity of a semiconducting material decreases with increasing temperture
Graph is a curve so R changes and I is changing fast than V. Increase temperature cause by larger current. P = I ^2R shows this. As R decrease so does resistivity. (4 marks)
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What is Kirchoff's second law?
The sum of e.m.f.s = sum of p.d.s in a closed loop. Energy is conserved. (2 marks)
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What is meant by a progressive wave?
Energy is transferred as a result of oscillations. (2 marks)
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2 differences between stationary and progressive waves
Progressive transfers energy and transfers shape/information (2 marks)
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Why do we use two slits to produce visible fringes on the screen rather than two separate identical light sources?
The light from two sources must be coherent and it is only possible to produce a constant phase difference using a single source. (2 marks)
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State the principle of superposition of waves
When two or more waves meet at a point. The displacement is equal to the sum of the displacements of each wave.
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Two adjacent transmitters are 1.0m apart with a receiving aerial R halfway between them. The transmitters emit coherent em waves of wavelength 3.0cm.
Original information for next question. Find diagram from electrons waves and photons june 2013.
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The student finds that the signal at the receiver R falls from max to zero when R is moved 0.75 cm towards a transmitter. Explain this observation. Make it clear how signal can be zero and why the distance moved is 0.75 cm.
The waves interfere. This produces a stationary wave with nodes and antinodes. The resultant signal is zero at a node. Distance from the max (antinode) to zero (node) is wavelength/4 which is 0.75 cm. 4 marks
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See Question 5bii) june 2013
Waves are polarised in vertical plane. Detected signal from T2 falls to zero when T2 rotated 90 degrees. Aerial receives singal from one transmitter. 3 marks
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What does coherent mean?
The waves have a constant phase difference between the waves.
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Why does amplitude decrease with distance and what is the relationship when sending a signal from a transmitter to a detector ? Refer to Question 5 June 2015 and the diagram for next 2 after.
The energy emitted by transmitters spreads out so less energy collected by receiver the further away it is.
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What effect on the intensity of the signal detected by a receiver when the amplitude of the waves emitted from a source is doubled.
Intensity increases by a factor of 4 as as intensity is directly proportional to amplitude squared.
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What effect on the intensity of the signal detected by a receiver when the detector is rotated 90 degrees about the axis.
Intensity falls to 0 as signal is vertically polarised and the receiver is in a position only to detect horizontally polarised signal.
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## Other cards in this set

### Card 2

#### Front

What is Kirchoff's second law?

#### Back

The sum of e.m.f.s = sum of p.d.s in a closed loop. Energy is conserved. (2 marks)

### Card 3

#### Front

What is meant by a progressive wave?

### Card 4

#### Front

2 differences between stationary and progressive waves

### Card 5

#### Front

Why do we use two slits to produce visible fringes on the screen rather than two separate identical light sources?