S2 Waves

Question 1

1. What are sounds caused by?

Answer 1

All sounds are caused by a vibrating object.

Question 2

2. Describe what happens to a wave trace when the amplitude, wavelength and frequency changes.

Answer 2

When the amplitude of a wave increases it gets taller.
When the wavelength of a wave increases it gets longer.
When the frequency of a wave increases there are more waves in the same time.
These can be seen on the following images:

Question 3

3. Describe how a sound changes when the frequency or amplitude is changed.

Answer 3

Higher pitched sounds have a higher frequency.
Louder sounds have a larger amplitude.

Question 4

4. State the frequency range of human hearing

Answer 4

The range of human hearing is approximately 20 Hz to 20 kHz (20 000 Hz)

Question 5

5. Describe what happens when the frequency of sound gets above the range of human hearing.

Answer 5

When the frequency of sound gets above the range of human hearing (above 20 kHz) it is called ultrasound. It still exists but humans can no longer hear it.

Question 6

5. Describe what happens to light when it undergoes refraction.

Answer 6

When light enters a different medium (material) it undergoes refraction. This means it changes speed and usually changes direction.

Question 7

6. Use the following terms correctly; normal, angle of incidence and angle of refraction.

Answer 7

The normal is a line at right angles to the surface where the light strikes it
The angle of incidence is the angle between the incident ray and the normal.
The angle of refraction is the angle between the refracted ray and the normal.
See Image.

Question 8

7. Describe the path of light as it passes from one medium to another at an angle to the surface.

Answer 8

When lights enters glass at an angle, it will bend towards the normal. (See image)
When light leaves glass at an angle it will bend away from the normal.

Question 9

7. Describe the path of light as it passes from one medium to another perpendicular to the surface.

Answer 9

When light enters glass perpendicular to the surface (along the normal), it goes straight through.

Question 10

8. Describe the shape of a diverging lens, and describe its effect on parallel rays of light.

Answer 10

A diverging lenses is thinner in the middle than the outside. It makes parallel rays diverge.

Question 11

8. Describe the shape of a converging lens, and describe its effect on parallel rays of light.

Answer 11

A converging lens is thicker in the middle than the outside. It makes parallel rays converge to a focus.

Question 12

9. Describe the image of a distant object produced by a converging lens

Answer 12

The image of a distant object produced by a converging lens is

a) smaller than the object,
b) vertically inverted and
c) horizontally inverted

Question 13

10. Describe how to measure the focal length of a converging lens.

Answer 13

The focal length of a converging lens can be measured as follows:
Start with the lens at the screen. Move it away until a sharp image of a distant object is obtained. Use a metre stick to measure the distance between the lens and the screen. This is the focal length of the lens.

Question 14

11. What effect does the curvature of a lens have on its optical power?

Answer 14

A lens with a greater curvature has a higher optical power.

Question 15

12. Explain the relationship between optical power and focal length.

Answer 15

A lens with a greater curvature will bend the rays more, so that they will come to a focus in a shorter distance. This means the focal length is shorter for a more powerful lens.

Question 16

13. State what the symbols stand for and what units go with each, for the formulae

P = 1/f

and

f = 1/P

Answer 16

P - Optical Power (D Dioptres)

f - Focal Length (m)

Question 17

13. What do negative and positive values of Optical Power indicate?

Answer 17

Negative values of Optical Power indicate a diverging lens.

Positive values of Optical Power indicate a converging lens.

Question 18

13. Example

Calculate the focal length of a lens with an optical power of 4 D.

Answer 18

f = ?
P = 4 D

f = 1/P
= 1/4
f = 0.25 m

(NB No need to convert to cm unless a question asks for the answer in cm.)

Question 19

13. Example

Calculate the optical power of a diverging lens with focal length 20cm.

Answer 19

f = 20 cm = 0.2 m
P = ?

P = 1/f
= 1/0.2
P = 5 D

Final answer is - 5 D since it is a diverging lens.

Question 20

14. Describe the function of the pupil of the eye.

Answer 20

The pupil lets light into the eye.

Question 21

14. Describe the function of the cornea of the eye.

Answer 21

The cornea is the covering over the front to protect the eye. It also starts to focus the light.

Question 22

14. Describe the function of the lens of the eye.

Answer 22

The lens brings the light to a focus on the retina.

Question 23

14. Describe the function of the retina of the eye.

Answer 23

The retina is the screen of the eye where a sharp image should be produced. It is filled with light sensitive cells.

Question 24

14. Describe the function of the optic nerve of the eye.

Answer 24

The optic nerve carries image information to the brain.

Question 25

15. Describe the effect of dim and bright light conditions on the pupil of the eye.

Answer 25

In dim light the pupil gets larger to let more light in.
In bright light the pupil gets smaller to let less light in.

Question 26

16. Explain what causes the blind spot in the eye, and explain the effect of this on your vision.

Answer 26

The blind spot is where the optic nerve meets the retina and there are no light sensitive cells. No image is produced here but the brain uses surrounding information to fill in what you see.

Question 27

17. Describe what happens to the image formed by a converging lens when the object is brought closer to the lens and use this to explain how our eyes view near and distant objects.

Answer 27

When an object is brought closer to a converging lens the image produced gets bigger. This is why distant objects appear smaller to our eye and near objects appear larger.

Question 28

18. Explain what is meant by accommodation of the eye and describe the shape of the lens of the eye when looking at near and distant objects.

Answer 28

Accommodation is the ability of the eye lens to change shape depending on how far away an object is.

When an object is distant the lens is thin;

when near the lens is thicker.

Question 29

19. Describe the nature of rays of light coming from near and distant object.

Answer 29

The rays of light coming from a distant object are parallel;

from a near object they are still diverging.

Question 30

20. Show on a diagram how rays of light should focus inside the eye if the object is in focus.

Answer 30

For a distant object, the rays arrive parallel. The lens is thin as the rays don’t need to bend much to meet at the retina.

For a nearby object, the rays are still diverging. The lens is thick as the rays do need to bend a lot to meet at the retina.