P2 Electric Circuits

Question 1

Define electric current

Answer 1

Electric current is the rate of flow of charge

Current = charge / time

(A) (Q) (t)

I = Q/t

Question 2

Define potential difference (voltage)

Answer 2

Potential difference is the energy supplied or transferred to each Coulomb of charge

potential difference = energy / charge

(V) (J) (C)

V = E / Q

Question 3

What is Ohm’s law?

Answer 3

potenial difference = current x resistance

(V) (A) (ohms)

V = I x R

Bigger resistance means means smaller current

Question 4

What are the important features of a series circuit?

Answer 4

• Current is the same everywhere in the circuit
• Total resistance is the sum of all the resistances (R = R₁ + R₂ + ….)
• Battery voltage is shared between the components (V = V₁ + V₂ + ….)

Question 5

What are the important features of a parallel circuit?

Answer 5

• the potential difference across each component is the same
• the total current through the whole circuit is the sum of the currents through the separate components (I = I1 + I2 + ….)

Question 6

What is the current-voltage (IV) characteristic of a filament lamp?

Answer 6

• As p.d. increases a greater current flows
• the filament wire heats up
• This means the resistance increases
• so the rise in current for each volt gets less

Question 7

What is the current-voltage (IV) characteristic of a diode?

Answer 7

• A diode allows current to flow one way only
• in the forward direction, as p.d. increases so does current
• in the reverse direction (turn the battery round) the diode has infinite resistance and so no current can flow

Question 8

How do we calculate the power output of a circuit?

Answer 8

Power = potential difference x current

(W) (V) (A)

P = I x V