# Year 11 Physics Exam Questions Part 1: The World Communicates

Posted on April 24, 2017 by DJ Kim

## Year 11 Physics Exam Questions: The World Communicates

Assess your depth of knowledge and understanding for the Year 11 Physics module ‘The World Communicates’ by answering the following exam style questions below.

You can refer to the Glossary of Key Words for the meaning of any verbs in the questions.

Detailed answers are provided at the bottom of this blog post.

What is a wave?

### Question 2

Describe a periodic wave in a string using the terms period, frequency, amplitude, wavelength and speed.

### Question 3

Compare transverse and longitudinal waves.

### Question 4

Here is a graphical representation of a wave in a string.

Answer the following questions
a.   What is the amplitude of the wave?
b.   What is the wavelength of the wave?
c.   What is the period of the wave?
d.   Can you find the speed of the wave from the information provided in the graph?

### Question 5

What could the y-axis be on a graph like the one in question 4 if you wanted to represent a sound wave instead? What would the crests and troughs correspond to?

### Question 6

Why can diffraction lead to interference?

### Question 7

Name the components of the electromagnetic spectrum, and for each name a device that can be used to detect the radiation.

### Question 8

Calculate the frequency of green light with a wavelength of 532 nm.

### Question 9

You stand at a certain distance from a source of light and measure its intensity. You then move three times further away and measure the intensity again. How will your two measurements differ?

### Question 10

Which wavebands cannot reach the ground from space, and why?

### Question 11

What is the difference between AM and FM communications channels, and why would you choose one or the other?

### Question 12

Identify some advantages and disadvantages of using microwaves for communications.

### Question 13

The diagram below shows an object placed in front of a concave mirror.

Describe the  nature of image formed and its location.

### Question 14

Name an application for each type of mirror:

(a) Plane Mirror

(b) Concave Mirror

(c) Convex Mirror

### Question 15

What is refraction and why does it occur?

### Question 16

If light is moving from air into glass with an angle of incidence of 30 degrees, what will the refracted angle be if the index of the glass is 1.57?

### Question 17

What is the meaning of a critical angle with regard to refraction?

### Question 18

Outline three types of communications systems that use electromagnetic waves which rely on reflection, and give examples of each one.

## Answers:

1. A wave is a propagating disturbance that carries and transfers energy.
2. A periodic wave consists of cycles that repeat:
a.   The period is the time it takes for one cycle of the wave to be completed, or how long it takes for one cycle to pass a point on the string.
b.   The frequency is how many cycles occur per second.
c.   The amplitude is the maximum displacement  of the string from the equilibrium position.
d.   The wavelength is the length one complete wave cycle, e.g. the distance between two crests.
e.   The speed of the wave is how fast the wave travels along the string, given by  velocity = frequency x wavelength.
3. In a transverse wave, the oscillation direction is perpendicular to the direction of wave propagation. In a longitudinal wave, the oscillation direction is parallel to the direction of wave propagation.
4. a.   The amplitude is 6 cm
b.   The wavelength is 20 cm
c.   The period cannot be determined from the graph, as it is a graph of displacement vs distance, not displacement vs time.
d.   No, the speed cannot be found.  As information about the frequency or period is required.
5. The y-axis could indicate pressure or the displacement of air molecules from their equilibrium positions. Crests would correspond to high pressure regions (compressions) and troughs would correspond to low pressure regions (rarefactions).
6. Diffraction causes waves to bend around obstacles and hence to spread out. If waves diffract they may end up becoming superimposed, superposition leads to interference.
7. Radio (detect with antennas), microwave (antennas), infra red (photodetectors), visible (eyes, photodiodes, film), ultraviolet (photodiodes, film), X-rays (photodiodes, film), gamma rays (photodiodes, film).
8. f = 5.6 x 1014 Hz
9. Intensity is inversely proportional to the square of the distance from the source. When you move 3 times further away, the power will decrease by 9 times.
10. Gamma rays, X-rays, most of the UV, some infra red and microwaves are absorbed by the atmosphere. Long wavelength radio waves are reflected by the ionosphere.
11. AM stands for Amplitude Modulation. The information is transmitted through changes in the amplitude of the wave. Each AM channel requires a smaller range of frequencies than FM, meaning you can have more AM channels in a given range of radio frequencies (bandwidth).
FM stands for Frequency Modulation. The information is transmitted through changes in the frequency of the wave. This is less susceptible to interference than AM resulting in better sound quality.
12. Advantages: Microwaves fall outside the radio spectrum, so offer new communications channels not already occupied by radio communications. Microwave channels can carry a large amount of information due to their higher frequency, and the wavelength is smaller meaning they require a smaller antenna.Disadvantages: Can be absorbed by different materials or affected by the atmosphere. Require a line-of-sight connection from the transmitter to the receiver.
13. The image will be real, inverted and diminished. It will be located between the centre and focus.
14. Plane mirrors – rear view mirrors in cars
Concave mirrors – satellite dishes
Convex mirrors – safety mirrors in car parks
15. Refraction describes the bending of a wave as it passes from one medium to another, which occurs due to a change in the speed of the wave.
16. 18.57 degrees.
17. When light is travelling from a higher refractive index material to a lower refractive index material, the refracted angle will be larger than the angle of incidence. When the angle of incidence is the critical angle, the refracted angle will be 90 degrees.
18. Radio waves used in radio communications are reflected off the ionosphere.
Microwaves and radio used in communications are concentrated by reflecting off satellite dishes to increase their strength.
Total internal reflection is used to transmit light over long distances in an optical fibre for telecommunications and the transmission of data on the internet.

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