The EM Spectrum

Question 1

What is the speed of light (and all other EM waves in a vacuum) ?

Answer 1

3 x 10^8 m/s

Question 2

What are electromagnetic waves composed of?

Answer 2

An electric field and magnetic field at right angles to each other

Question 3

What are the dangers of gamma rays and x-rays?

Answer 3

• Can cause mutations to the DNA in cells in the body
• This may kill the cells or cause cancer

Question 4

What are the dangers of ultraviolet?

Answer 4

• UV in sunlight can damage skin cells causing sunburn
• Over time exposure to UV can cause skin cancer
• Can also damaged the eyes leading to eye conditions

Question 5

What are the dangers of infrared?

Answer 5

- Transfers thermal energy, too much can cause skin burns

Question 6

What are the dangers of microwaves?

Answer 6

• They heat water so they can heat water inside our bodies
• Heating cells can damage or kill them

Question 7

What are the dangers of radio waves

Answer 7

None

Question 8

What are the uses of gamma rays?

Answer 8

• Sterilise food and medical equipment
• In scanners to detect cancer
• Treat cancer

Question 9

What are the uses of x-rays?

Answer 9

• Do you look inside objects including medical x-rays to look inside bodies
• In airport security scanners to see what people have in their luggage

Question 10

What are the uses of ultraviolet?

Answer 10

• To detect security marks made using special pens
• Inside fluorescent lamps
• To detect forged banknotes, real banknotes have markings that glow in UV light
• To disinfect water

Question 11

What are the uses of visible light?

Answer 11

• Allow us to see
• Photography

Question 12

What are the uses of infrared?

Answer 12

• In cooking
• To make a thermal images, used by police and rescue services
• In short range communications such as between laptops
• Remote controls for TVs and other appliances
• To send information along optical fibres
• In security systems such as burglar alarms to detect people moving around

Question 13

What are the uses of microwaves?

Answer 13

• In mobile phones and communicate by satellite transmissions
• For cooking

Question 14

What are the uses of radio waves?

Answer 14

• Broadcasting radio and TV programmes
• Communicating with ships aeroplanes and satellites

Question 15

Why was the gold foil experiment conducted in a vacuum?

Answer 15

• So they knew that any deflections of the alpha particles were because of collisions with the gold foil and not due to deflections off anything else

Question 16

What were the results of the gold foil experiment?

Answer 16

• Most alpha particles passed straight through the foil
• Small number of alpha particles deflected by large angles (>40 degrees)
• A very small number of aplha particles came straight back off the foil

Question 17

What did Rutherford conclude after the gold foil experiment?

Answer 17

• The atom is mostly empty space (most went straight through)
• There is a concentration of positive charge in the atom (positive alpha particles were repelled by positive charges at large angles)
• The positive charge and mass are concentrated in a tiny volume in the atom (only a very small number of particles were directly deflected back)

Question 18

Radio waves… electrical circuits

Answer 18

Radio waves can be produced by, or themselves induce, oscillations in electrical circuits

Question 19

How do you investigate refraction in rectangular glass blocks?

Answer 19

• Place the block on A3 paper and draw around it 
• Draw the normal line, which will be at right angles to the side of the block
•  Use a ray box to shine the light at the point where the normal meets the block
• Using a pencil, mark where the incidence ray enters the block and where the ray leaves the block
• Connect the two dots, measure the angle from the normal
• Collect the data and compare 

Question 20

How do you investigate the relationship between the rate at which material radiates thermal energy and the nature of its surface?

Answer 20

• Fill Leslie’s cube with hot water at a known temperature, plug the top
• Place a thermometer a small distance away from each side
• Measure the temperature at a distance of 10 cm from each side for 5 min, taking a reading every 30 sec
• Plot the results on a graph

Question 21

How do you investigate the relationship between the rate at which material absorbs thermal energy and the nature of its surface?

Answer 21

• Fill Leslie’s cube with cold water at a known temperature, plug the top with bung and thermometer
• Heat each side with a radiant heater from the same distance away (about 10 cm)
• Record how the temperature of the water changes, every 30 sec, over a period of time
• Plot results on a graph