Charge, Current, and Potential Difference

Question 1

What is current? What does it depend upon?

Answer 1

Current is the movement of charged particles per second and this depends on…

• The speed particles move at.
• The number of particles.
• The charge on each.

Question 2

Describe why drift velocity is needed, and what this is.

Answer 2

Particles of charge collide in a wire. Drift velocity describes the average speed travelled by charge in a wire by the electrons overall, as opposed to each one, as the speed of each is much slower.
I = vAnq
V = Drift velocity ms^-1
A = Cross-sectional area of wire, (m^2).
n = Density of charge, charge carried per m^3, (Cm^-3)
q = charge on each carrier.

Question 3

The number of charge carriers per cubic meter depends on the …. Metals have …., semi-conductors have far fewer carriers, and at low voltages insulators have no free electrons so no … can flow.

Answer 3

Material, lots, current.

Question 4

Sensors detect …. Thermistors detect a change in … which causes the …. to increase, and a temperature …. uses this change to calculate the new ….

Answer 4

Changes, temperature, resistance, sensor, current.

Question 5

What is current? What is the formula used?

Answer 5

Current is the number of charged particles, (rate), that flow in a set time past a set point. The formula is I (current) = Q (charge) / t (time)
A charge of 1C means that a current of 1A carries this charge per second.

Question 6

What is conventional current compared to the flow of electrons? What measures the current?

Answer 6

Conventional current is how charge particles move from the positive to negative terminal. Electrons flow in the opposite direction. Ammeters measure current.

Question 7

What is potential difference and what formula describes this?

Answer 7

This is the energy transferred per unit charge and can be defined as V (voltage) = W (work done) / Q (charge).
When 1J of energy is transferred by moving 1C of charge through the component, this makes the voltage 1V.
IV = 1JC^-1.
A voltmeter measures this in parallel.

Question 8

What is power and what formula defines this?

Answer 8

Power is the rate of transfer of energy. This is measured in watts, where 1J transferred each second is 1 watt.
Power = IV (current * voltage) when current is the number of charge particles transferred per second and voltage is energy transferred divided by charge. It can also be defined as P = W / t (work done in joules / time in seconds).

Question 9

What is the formula for work done?

Answer 9

W = Pt
Power = VI
so W = VIt