(14) EM Spectrum

Question 1

(Q) The higher the frequency of an EM wave, the

A More energetic and more able to penetrate media than low frequency waves
B Less energetic and more able to penetrate media than low frequency waves
C More energetic and less able to penetrate media than low frequency waves
D Less energetic and Less able to penetrate media than low frequency waves

Answer 1

A

Question 2

(Q) High frequency EM waves can

A carry less information
B carry more information
than low frequency EM waves.

Answer 2

B

Question 3

(Q) Name 3 properties of EM waves

Answer 3

Any 3 from
1. EM waves are transverse waves
2. EM waves can travel in vacuum (or: EM waves do not require a medium to travel)
3. They travel at the same speed in a vacuum (3.0x10^8 m/s)
4. They transfer energy from one place to another
5. they all obey the wave equation,
v=f入
6. EM waves obey the laws of reflection and refraction
7. EM waves do not carry any electric charges.

Question 4

(Q) When an EM wave travels from one medium to another, what changes and what does not change?

Answer 4

Speed and Wavelength change, frequency does not change.

Why? frequency is dependent on the source,
speed depends on medium,
wavelength depends on speed

in this case, only the medium is changed, not the source.

Question 5

(Q) How are EM waves produced?

Answer 5

When a charge is accelerated.

Question 6

(Q) Name the types of an EM wave in order of increasing frequency.

Answer 6

Radio Waves
Microwaves
Infrared (IR) radiation
Visible light 
Ultraviolet (UV) Radiation
X-rays
Gamma rays

Note: this is also the order in DECREASING wavelength.

Question 7

(Q) Name the types of an EM wave in order of increasing wavelength.

Answer 7

Gamma Rays
X-Rays
Ultraviolet (UV) radiation
Visible light 
Infrared (IR) radiation
Microwaves
Radio waves

Also the order in DECREASING frequency.

Question 8

(Q) Name the components of visible spectrum of Light.

Answer 8

Red
Orange
Yellow
Green
Blue
Indigo
Violet

Note: this is the order in INCREASING frequency, and DECREASJNG wavelength.

Question 9

(Q) Name 2 uses of radio waves.

Answer 9

Any 2 from

1. radio communication
2. television transmission
3. telephone transmission

Question 10

(Q) Name 2 uses of Microwaves.

Answer 10

Any 2 from:

1. Satellite television
2. Microwave ovens
3. Radar system to detect ships, aircraft and missiles

Question 11

(Q) State 2 uses of Infra-red radiation.

Answer 11

Any 2 from

1. Ear thermometers
2. Intruder alarm
3. Infra-red remote controllers

Question 12

(Q) State 2 uses of visible light.

Answer 12

1. Optical fibres for medical uses (to carry internal organ images to doctors)
2. Telecommunications (carrying signals/data for telecommunication purposes through optical fibres)

Question 13

(Q) State 2 uses of Ultraviolet (UV) Radiation.

Answer 13

1. Sunbed (for artificial tanning)
2. Sterilisation of medical equipment

Also: Forgery detection (but difficult to explain), washing powders, fluorescent tubes

(concept: fluorescence)

Question 14

(Q) State 2 uses of X-rays.

Answer 14

Any 2 from:

1. Security check at airport
2. Radiology (for radiation therapy in cancer treatment)
3. Radiography (to locate fractures in bone)

Question 15

(Q) State 2 uses of Gamma Rays.

Answer 15

1. Radiation therapy (for cancer treatment)
2. Gamma Knife Radiosurgery (targeting only specific spots but insufficient to damage surrounding cells)

In short, MEDICAL TREATMENT

Question 16

(Q) State the effects of EM waves on cells and tissue.

Answer 16

Higher frequency EM waves like X Rays and Gamma rays carry greater amounts of energy and are classified as Ionising Radiations. (the rest are non-ionising radiations)

Ionisation harms living cells resulting in destruction or modification of living tissues. Widespread damage if cells kills people.

Ionisation may result in growth of cancer cells and leading to tumors.