Noir et Blanc

Question 1

How to convert from kelvin to degrees

Answer 1

subtract 273

Question 2

How to convert from degrees to kelvin

Answer 2

Add 273

Question 3

What is absolute zero? What is it in kelvin?

Answer 3

• The coldest anything can get, the particles has as little energy as is possible (-273 degrees)
• It is 0k

Question 4

Explain why electrical energy is transmitted using a very high voltage. (5)

Answer 4

(M1) A high voltage leads to a low current
(M2) Because power = current x time
(M3) As a result, less energy is lost from the wire in the form of heat energy as the wires will not heat up as much due to a high current
(M4) This makes it more efficient
(M5) Because less current is flowing a thinner wire can be used without building up a large resistance

Question 5

What is the unit for momentum?

Answer 5

kg m/s

Question 6

What determines how much a wave is diffracted?

Answer 6

The wavelength of the wave compared with the size of thr gap.

• If the gap is much bigger than the wavelength there will be no diffraction.
• If the gap is the same as the wavelength then there will be maximum diffraction.

Question 7

what are the two conditions needed for total internal reflection?

Answer 7

• Change in density of medium/ optically dense material

- The angle of incidence being larger than the critical angle

Question 8

What happens is the angle of incidence is:

• less than the critical angle
• The same as
• Bigger than

Answer 8

• Less than: Rays are only partially internally reflected but most passes out
• Equal to: emerging ray comes out along the line of the surface and quite a lot is internally reflected
• More than: No light comes out. It is totally internally reflected.

Question 9

Which device can be used to display sound waves?

Answer 9

An oscilloscope

Question 10

What is the effect of a changing amplitude on a sound wave?

Answer 10

• The greater the amplitude of a wave or vibration, the more energy it carries.
• This means it will be louder.

Question 11

Explain the connection between frequency and pitch in a sound wave.

Answer 11

• The frequency is the number of complete vibrations each second.
• If the wave vibrates with a high frequency, the sound is high pitched.
• If the wave vibrates with a low frequency, the sound is low-pitched.

Question 12

Describe how to measure frequency on an oscilloscope.

Answer 12

• adjust the time division setting on the horizontal axis until the display shows at least one complete cycle
• Read off the time period (the time taken for one complete wave/ cycle to pass)
• Use equation frequency = 1/ time period to find the frequency

Question 13

what is the key principle of friction?

Answer 13

Friction increases as speed increases

Question 14

Describe what happens when a volt develops in a circuit.

Answer 14

FAULT - live wire touches the metal casing resulting in a big surge in current to the earth.
SURGE - this surge draws a large current through the live wire
The current raise the temperature of the circuit and the fuse melts
SAFETY - the fuse melting isolates the appliance from the live and so protects user from electric shocks.

Question 15

What is the rule about current in a series circuit?

Voltage?

Answer 15

• The same current flows through each component

- Voltage is shared through the components

Question 16

What is the rule of current in parallel circuits?

Voltage?

Answer 16

• The current is split

- The voltage is the same in each component.

Question 17

What does a gold leaf electroscope do?

Answer 17

• It determines the size of the charge on an object by how much the gold leaf moves (i.e. how much it is repelled or attracted by the object)