Mechanical
What is the equation for gravitational potential energy?
Ep = mgh
Which direction does heat energy move?
From hotter objects to colder objects.
What is the type of electricity you get by rubbing a balloon on your head?
Static electricity.
How much energy is used by a 60W bulb in 2 minutes?
t = 2*60 = 120s
E = Pt
E = 60 x 120
E = 7200J
What type of energy does a stretched rubber band have?
Elastic potential energy
What is the weight of a 5kg cat?
50N
Slope up to 0degC and then flat, then slope up to 20degC.
What is the definition and unit of current?
The flow of electrons, measured in Amps (or Amperes)
What is the energy efficiency of an LED bulb that produces 35J of light energy but uses 50J?
70%
(35/50 x 100)
Name three forms of potential energy.
Chemical, elastic, gravitational
Picture a full supermarket trolley. It is easier to push it up a ramp than lift it up. The work done is the same, so why is the force different?
W = Fd
If the distance is greater (ramp is longer than lift) then the force can be lower to do the same amount of work.
Describe the process of convection, including density, in a boiling kettle.
Heat energy at the bottom increases space between water particles, making it less dense. Hot water rises above the heat source, cools, particles moving closer together and it becomes more dense and sinks.
A 12V battery is connected to two parallel branches, each containing two bulbs. Assuming all bulbs are equal, what will the voltage be across one bulb?
6V
How much energy is used to heat 5kg ethanol from 20degC to 78degC, if its specific heat capacity is 2.46?
Q = mcT
Q = 5 x 2.46 x 58
Q = 713.4J
What is the Law of Conservation of Energy?
Energy cannot be created or destroyed, it can only be transferred or transformed.
What will the energy bar chart of a leaf falling off a tree look like one quarter of the way down?
3/4 height Ep, 1/4 height Ek (possibly a tiny part to heat energy from friction)
Insulation - space between the inner and out layers reduces heat loss by conduction and convection.
Silver lining/cover - reduces heat loss by radiation by reflecting heat back into drink.
What is the resistance of a fuse that is designed to fail at 10A when connected to a 240V power supply?
24 Ohms
What is the resistance of a bulb that has a power rating of 25W when supplied with a 2A current?
6.25 Ohms
V=P/I=25/2=12.5 R=V/I=12.5/2=6.25 Ohms
Which law is an energy bar chart trying to visualise?
Conservation of energy
Why does a bungy jumper not get back to the height of the platform? Name the energy transformations involved.
Jumper starts with maximum GPE, jumps and it turns to kinetic then elastic energy, they bounce back up ( kinetic) and stop at top where it is GPE again. There is less GPE because some has been lost as heat and sound energy, so final height is lower.
What steps would I need to take to calculate the total energy needed to turn 20degC water to a gas? Give equations.
1) Q=mcT to find energy to change temp by 80degC to get to 100degC
2) Q = mL to get energy to turn liquid to gas
3) Add them together
Use formulae to explain what is different about a low power bulb that can use the same voltage as a normal one.
P=VI - if power is lower but voltage is the same, the current must be lower.
To have a lower current and the same voltage, the resistance must be higher V = IR
How fast is an 8kg bowling ball travelling just before it hits the ground after falling off a 1.2m bench?
4.9ms-1
(Ep = 96 = Ek, rearrange to get v)
Name for energy which includes visible light, x rays, gamma rays and radio waves.
Electromagnetic energy