Physics - PPQ Flashcards
Where is the centre of gravity in an object?
Directly above the point of which weight acts from
Half way between the top and bottom of the object
How does the water pumped into the cooling tower cool down?
- Temperature is proportional to average kinetic energy
- As the water turns into a gas, the highest energy particles leave the liquid:
- Kinetic energy of gas increases, kinetic energy of water decreases,
- Therefore temperature of the water decreases
How do you find out the weight of an object?
Use an electronic balance to find the mass
Use W=mg
What is the principal of moments?
Total anti-clockwise moment = total clockwise moment
for a system to be in equilibrium
What are the equivalent units for pressure?
Pa and N/m^2
What does the flat part of a velocity-time graph say about the forces acting on a falling object?
Resultant forces = 0
Acceleration = 0
If a charged object comes into contact with a metal object, what happens?
The electrons are transferred to the metal
As metals are conductors
Such that the charge has been earthed
Using ideas about momentum, why does a cannon move in the opposite direction to the cannonball?
- Each action has an opposite and equal reaction
- Momentum before = 0
- Momentum is conserved, therefore total momentum after = 0
- M=mv
How can you keep a wire at a constant temperature?
Use a switch
Use a low current
Use a water bath
Only turn the current on for a short time
Why is a filament lamp likely to fail when it is first switched on?
The filament heats up very rapidly
Causing it to melt
How does a turbine and generator produce electricity?
Turbine spins
Causing a coil of wire to spin between the poles of magnets
Inducing a current across the wire
Why is it important for a turbine to turn at a constant speed?
To keep the current produced constant
How is nuclear fission different from radioactive decay?
- Decay is random, fission is not
- Fission produces 2 daughter nuclei, decay produces 1
- Decay emits alpha and beta particles, fission doesn’t
- Rate of decay can’t be altered, rate of fission can
- Fission requires an input particle, decay doesn’t
How does a black container and shiny container differ when it comes to radiation of thermal energy?
Black absorbs radiation
Shiny reflects radiation
Black is a good emitter of radiation
Shiny is a bad emitter of radiation
What is the difference between vector and scalar quantities?
Scalar have only magnitude
Vector have magnitude and direction
What is the difference between a linear and non-linear relationship?
Linear is a straight line, non-linear is a curve
What energy transfers take place when a car slows by its brakes?
Kinetic of the car
to the thermal of the breaks and surroundings
mechanically or by heating
Why is the stopping distance less when going uphill rather than on a flat road?
The weight of the car acts to create a larger deceleration force, slowing the car down quicker
How is the current spread through a circuit?
The current is split evenly over wires in parallel
The current is the same over wires in series
How is the voltage spread through a circuit?
The voltage is split evenly over wires in series
The voltage is the same over wires in parallel
What is the relationship between how convection currents occur in air and in a liquid?
They are the same
How is the evolutionary path of a low mass star different to that of a high mass star?
Low mass star:
- On the main sequence for a longer time
- Becomes a red giant
- Becomes a white dwarf
High mass star:
- On the main sequence for a shorter time
- Becomes a red supergiant
- Becomes a neutron star or a black hole
What is required to measure the count rate of a radioactive source?
GM tube connected to a counter
What effect does the emission of a gamma ray have on an isotope’s nucleus?
No effect, as the proton and neutron numbers don’t change, because a gamma ray is an electromagnetic (EM) wave
