electricity equations

Question 1

what is the equation for power

Answer 1

power = energy transferred / time
power = work done / time
power = potential difference × current
power = (current)2 × resistance

Question 2

what is the equation for efficiency

Answer 2

efficiency = useful output energy / total input energy
efficiency = useful power output / total power input

Question 3

what is the equation for wave speed

Answer 3

wave speed = frequency × wavelength

Question 4

what is the equation for charge flow

Answer 4

charge flow = current × time

Question 5

what is the equation for PD

Answer 5

potential difference = current × resistance

Question 6

what is the equation for energy transferred

Answer 6

energy transferred = power × time

energy transferred = charge flow × potential difference

Question 7

Why is a system not 100% efficient?

Answer 7

Some energy is always wasted

Question 8

In a light bulb, 25J of energy is supplied. 5J are usefully transferred into light energy.
What is the efficiency of the bulb?

Answer 8

5/25 = 0.2 x100 = 20%

Question 9

What is a renewable resource?

Answer 9

One that won’t run out - we can replace as fast as we use it.

Question 10

What is finite resource?

Answer 10

One that will run out (non-renewable)

Question 11

Name 3 fossil fuels.

Answer 11

Coal, oil, gas

Question 12

List the 8 energy stores?

Answer 12

Thermal, Kinetic, Gravitational Potential, Elastic potential, Chemical, Magnetic,
Electrostatic, Nuclear

Question 13

What is the value for gravity on Earth?

Answer 13

9.8 (unless they tell you to use a different number for gravity!)

Question 14

What are the advantages and disadvantages of a nuclear power station?

Answer 14

:) - Cheap source of energy, get a lot of energy, reliable

:( - finite, nuclear waste is dangerous, expensive to decommission

Question 15

What different ways we can get energy (energy resources)?

Answer 15

Coal, oil, gas, nuclear, wind, hydro-electricity, solar, bio-fuel, tides, geothermal