Physics - PPQ

Question 1

Where is the centre of gravity in an object?

Answer 1

Directly above the point of which weight acts from

Half way between the top and bottom of the object

Question 2

How does the water pumped into the cooling tower cool down?

Answer 2

1. Temperature is proportional to average kinetic energy
2. As the water turns into a gas, the highest energy particles leave the liquid:
3. Kinetic energy of gas increases, kinetic energy of water decreases,
4. Therefore temperature of the water decreases

Question 3

How do you find out the weight of an object?

Answer 3

Use an electronic balance to find the mass

Use W=mg

Question 4

What is the principal of moments?

Answer 4

Total anti-clockwise moment = total clockwise moment

for a system to be in equilibrium

Question 5

What are the equivalent units for pressure?

Answer 5

Pa and N/m^2

Question 6

What does the flat part of a velocity-time graph say about the forces acting on a falling object?

Answer 6

Resultant forces = 0

Acceleration = 0

Question 7

If a charged object comes into contact with a metal object, what happens?

Answer 7

The electrons are transferred to the metal
As metals are conductors
Such that the charge has been earthed

Question 8

Using ideas about momentum, why does a cannon move in the opposite direction to the cannonball?

Answer 8

1. Each action has an opposite and equal reaction
2. Momentum before = 0
3. Momentum is conserved, therefore total momentum after = 0
4. M=mv

Question 9

How can you keep a wire at a constant temperature?

Answer 9

Use a switch
Use a low current
Use a water bath
Only turn the current on for a short time

Question 10

Why is a filament lamp likely to fail when it is first switched on?

Answer 10

The filament heats up very rapidly

Causing it to melt

Question 11

How does a turbine and generator produce electricity?

Answer 11

Turbine spins
Causing a coil of wire to spin between the poles of magnets
Inducing a current across the wire

Question 12

Why is it important for a turbine to turn at a constant speed?

Answer 12

To keep the current produced constant

Question 13

How is nuclear fission different from radioactive decay?

Answer 13

1. Decay is random, fission is not
2. Fission produces 2 daughter nuclei, decay produces 1
3. Decay emits alpha and beta particles, fission doesn’t
4. Rate of decay can’t be altered, rate of fission can
5. Fission requires an input particle, decay doesn’t

Question 14

How does a black container and shiny container differ when it comes to radiation of thermal energy?

Answer 14

Black absorbs radiation
Shiny reflects radiation

Black is a good emitter of radiation
Shiny is a bad emitter of radiation

Question 15

What is the difference between vector and scalar quantities?

Answer 15

Scalar have only magnitude

Vector have magnitude and direction

Question 16

What is the difference between a linear and non-linear relationship?

Answer 16

Linear is a straight line, non-linear is a curve

Question 17

What energy transfers take place when a car slows by its brakes?

Answer 17

Kinetic of the car
to the thermal of the breaks and surroundings
mechanically or by heating

Question 18

Why is the stopping distance less when going uphill rather than on a flat road?

Answer 18

The weight of the car acts to create a larger deceleration force, slowing the car down quicker

Question 19

How is the current spread through a circuit?

Answer 19

The current is split evenly over wires in parallel

The current is the same over wires in series

Question 20

How is the voltage spread through a circuit?

Answer 20

The voltage is split evenly over wires in series

The voltage is the same over wires in parallel

Question 21

What is the relationship between how convection currents occur in air and in a liquid?

Answer 21

They are the same

Question 22

How is the evolutionary path of a low mass star different to that of a high mass star?

Answer 22

Low mass star:

1. On the main sequence for a longer time
2. Becomes a red giant
3. Becomes a white dwarf

High mass star:

1. On the main sequence for a shorter time
2. Becomes a red supergiant
3. Becomes a neutron star or a black hole

Question 23

What is required to measure the count rate of a radioactive source?

Answer 23

GM tube connected to a counter

Question 24

What effect does the emission of a gamma ray have on an isotope’s nucleus?

Answer 24

No effect, as the proton and neutron numbers don’t change, because a gamma ray is an electromagnetic (EM) wave

Question 25

What is the formula for pressure difference?

Answer 25

Pressure = height x density x g

Question 26

When you measure the temperature across a thermistor, what do you need to ensure?

Answer 26

• Stirring to spread the heat
• Placing the thermometer directly next to the thermistor both horizontally an vertically
• Place the heat source and thermistor in the middle of the water

Question 27

How does a velocity-distance graph support the Big Bang theory?

Answer 27

• Larger velocity has a larger red shift
• Big Bang states that the universe is expanding
• Seen as the further away galaxies have a larger velocity

Question 28

How can microwaves cause damage to the human body?

Answer 28

Internal bleeding / heating of internal cells

Question 29

How can radio waves cause damage to the human body?

Answer 29

Probably no harm / no damage caused

Question 30

How can IR waves cause damage to the human body?

Answer 30

Skin burns

Question 31

How can visible light cause damage to the human body?

Answer 31

Damage to vision

Question 32

How can UV waves cause damage to the human body?

Answer 32

Skin cancer

Question 33

How can x-rays cause damage to the human body?

Answer 33

Mutate/kill cells

Question 34

How can gamma waves cause damage to the human body?

Answer 34

Mutate/kill cells