Light and EM Spectrum

Question 1

Reflection of Light

Answer 1

Waves can be reflected at the boundary between 2 materials. The angles of incidence and reflection are measured between the light ray and the normal (Measured at right angles to the air/glass)

Question 2

Diffuse reflection

Answer 2

If a surface is rough, diffuse reflection happens. Instead of forming an image the reflected light is scattered in all directions.

Question 3

Total internal reflection

Answer 3

When a light ray reaches the boundary between two transparent materials it may be refracted. If it is leaving the more dense medium, this refraction would be expected to bend the ray away from the normal as it emerges.

However, if this would bring the ray out at more than 90° from the normal, the refraction is not possible. In this situation, the ray is reflected inside the more dense medium, following the law of reflection.

This is called total internal reflection (TIR). The angle of incidence when the ray changes from just refracting to TIR is called the critical angle.

Question 4

Colour

Answer 4

Range of colours - Increase in Frequency and decreasing wavelength.

Red
Orange
Yellow
Green
Blue
Indigo
Violet.

Question 5

EM Waves

Answer 5

EM waves are transverse waves. Their vibrations or oscillations are changes in electrical and magnetic fields.

Question 6

Radio waves

Answer 6

Used for communication such as broadcasting TV and Radio

Transmitted easily though air, they do not cause damage to the human body and can be reflected.

Question 7

Microwaves

Answer 7

Used for cooking food, Communications and satellite communications. Intense sources can heat body cells

High frequency Microwaves have frequencies that are easily absorbed by molecules in food. The internal energy of the molecules in food increases, this causes heating

Question 8

Infrared

Answer 8

Usually used by electrical heaters, cookers for cooking food, short range communications like remote controls, security systems etc. The heating effect of IR can cause burns to the skin

It has frequencies that are absorbed by some chemical bonds. The absorption heats the bonds. ALL objects emit infrered light. This is good for thermal imaging, to see people in the dark

Question 9

Visible light

Answer 9

Light we can see. Used in illumination and photography as well as fibre optic communications.

Question 10

UV

Answer 10

UV can cause skin to tan or burn. UV is ionising. The hazardous properties means it will kill bacteria and can be used for disinfecting water.

Question 11

EM waves in Medicine

Answer 11

High energy waves are transmitted through body tissue without issue, this makes them ideal for internal imaging. X-Rays are absorbed by structures like bones which is why we use them for internal image scanning.

Question 12

Ionising Radiation

Answer 12

UV waves, X-Rays and gamma rays are all ionising. They can add or remove electrons from molecules producing electrically charged ions.

UV waves can cause damage to skin and eyes and increase the risk of skin cancer.
X-Rays and Gamma rays can cause the mutation of genes

Question 13

Emission and absorption of Infrared

Answer 13

All bodies emit and absorb infrared radiation. The hotter the body the more IR it gives off, The greater the proportion of emitted radiation is visible light