Section 3: Light and sound

Question 1

What are light waves?

Answer 1

Transverse waves which can be reflected, refracted and diffracted

Question 2

refraction

Answer 2

Light waves change speed when they pass through objects of different densities, this causes them to change direction. When they return to the original density they will continue in the original direction.

Question 3

reflection

Answer 3

Light hitting a reflective surface will ‘bounce’ back from the surface (at the same angle they hit the surface.)

Question 4

diffraction

Answer 4

When light meats a barrier, it will carry on through the gap and spread out in the area beyond.

Question 5

What is the law of reflection?

Answer 5

The angle of incidence is the angle that light hits a mirror; it is taken between 90 degrees from the mirror and the incidence wave (the wave that hits the mirror.)

The angle of reflection is the angle that light leaves the mirror; it is taken between 90 degrees from the mirror and the angle of reflection.

The angle of incidence is always the same as the angle of reflection.

Question 6

Describe an experiment to determine the refractive index of glass using a glass block

Answer 6

Shine a ray of light through a glass block, measure the angle of incidence and the angle of refraction.
Do sin(i) divided by sin(r) and you will have the refractive index of glass.

Question 7

Describe experiments to investigate the refraction of light, using rectangular blocks, semicircular blocks and triangular prisms

Answer 7

Place a block of glass on a piece of paper, drawing an outline.
At one point, draw the normal line.
Draw a line at 30 degrees to the normal line, shine a ray of light down this line.
Draw a line where the light comes out the other side. Connect the two lines, drawing the refracted ray.
Measure the angle of the emergent ray.
Repeat for different shaped glass.

Question 8

What is the relationship between refractive index, angle of incidence and refraction

Answer 8

refractive index = angle of incidence / angle of refraction

n = sin i / sin r

Question 9

Describe the role of total internal reflection in transmitting information along optical fibres and in prisms

Answer 9

Beyond the critical angle, light will be reflected back into the medium they came from at the same angle. In this way they are trapped in the medium.
By reflecting light past its critical angle you can make it travel through a medium to send information: this is done in optical fibres

Question 10

What is the critical angle?

Answer 10

The angle of incidence at which maximum refraction occurs

Question 11

Analogue signals

Answer 11

The amplitude and/or frequency constantly vary.

Question 12

Digital signals

Answer 12

Consists of pulses with two states: on; off

Question 13

What is the relationship between the critical angle and refractive index?

Answer 13

sin c = 1 / n

sin (critical angle) = 1 / refractive index

Question 14

What are the advantages of using digital signals ?

Answer 14

As signals get transmitted, they become weaker and need to be amplified. Regeneration of digital signals create a clean, accurate copy of the original.

However regeneration of analogue signals also amplify any accompanied noise, which may create errors in the signal.

Question 15

What are sound waves?

Answer 15

Longitudinal waves which can be reflected, refracted and diffracted

Question 16

What is the frequency range for human hearing?

Answer 16

20 Hz - 20 000 Hz

Question 17

Describe an experiment to measure the speed of sound in air

Answer 17

Measure the distance between two places, have a sound made in one place, as soon as you see the sound has been made start a stop watch, as soon as you hear the sound made stop the stopwatch.

distance/time= speed

Question 18

How is an oscilloscope and microphone used to display sound waves?

Answer 18

A microphone detects sound waves, it can feed this information into an oscilloscope which will display it as a wave (or straight line.)

Question 19

Describe an experiment using an oscilloscope to determine the frequency of a wave

Answer 19

Have an noise made into a microphone attached to an oscilloscope, for example have someone try to sing a note. See how many oscillations there are per second, this will be your frequency. Try changing the pitch of the note and see it the number of oscillations per second changes.

An oscillation is the completion of one wave i.e from one peak and the next.

Question 20

What does the pitch of sound depend on?

Answer 20

The frequency of vibration of the source

Question 21

What des the loudness of a sound depend on?

Answer 21

The amplitude of vibration

Question 22

What does sound require?

Answer 22

A medium to transfer energy