P7. Rays & Waves

Question 1

Monochromatic light

Answer 1

Light of a single frequency

Question 2

Normal

Answer 2

A line perpendicular to the mirror surface where the reflection occurs

Question 3

Laws of reflection

Answer 3

1. Angle of incidence = angle of reflection

2. The incident ray, the reflected ray and the normal all lie in the same plane

Question 4

Refraction

Answer 4

The bending of light when it passes from one medium to another

Question 5

Laws of refraction

Answer 5

1. Snell’s Law - refractive index is the ratio of sin i / sin r
2. The incident ray, refracted ray and the normal all lie in the same plane

Question 6

Critical angle

Answer 6

The angle of incidence in the denser medium when the angle of refraction in the less dense medium is 90°

Question 7

Characteristics of image formed by a plane mirror

Answer 7

1. Same size
2. Laterally inverted
3. Upright
4. Virtual (cannot be projected onto a screen)
5. Object and image have the same distance from mirror

Question 8

Uses of optical fibres

Answer 8

1. Used in telecommunications as optical fibres can carry enormous amounts of information at very high speeds in light pulses trapped inside them
2. Used in endoscopes that allow surgeons to examine patients’ internal organs

Question 9

As the object distance decreases…

Answer 9

As the object distance decreases, the image distance increases and the image size increases

Question 10

Features of EM waves

Answer 10

1. Can travel through a vacuum / do not need a medium
2. Travel through a vacuum at the speed of light
3. Are transverse waves
4. Transfer energy

Question 11

Uses of radio waves

Answer 11

1. Radio stations
2. Televisions
3. Cordless phone signals
4. Airplane communications

Question 12

Uses of microwaves

Answer 12

1. Mobile phones
2. Satellite television
3. Heating effect used in microwave ovens
4. Police radar

Question 13

Uses of infra-red waves

Answer 13

1. TV remote controllers
2. Intruder alarms
3. Electrical appliances, eg. grills, radiant heaters

Question 14

Uses of ultraviolet rays

Answer 14

1. Kill bacteria

2. In black light to find blood and saliva

Question 15

Uses of X-rays

Answer 15

1. See broken bones

2. In airport security systems to look for hidden objects

Question 16

Uses of gamma rays

Answer 16

1. Treat cancer
2. Sterilise medical equipment
3. Check for leaks in pipes
4. Smoke detectors

Question 17

Safety issues of microwaves

Answer 17

Microwaves can cause internal heating of body tissues

Question 18

Safety issues of infra-red radiation

Answer 18

Infra-red radiation can cause skin burns

Question 19

Safety issues of ultraviolet rays

Answer 19

Overexposure to ultraviolet rays increases the risk of skin cancer

Question 20

Safety issues of X-rays and gamma rays

Answer 20

X-rays and gamma rays are ionising radiation that can cause mutations leading to cancer
*ionising radiation strips electrons from atoms in their path so the atoms become ions