M4C3

Question 1

What is Kirchhoff’s first law?

Answer 1

The sum of all currents entering a junction is equal to zero (a current leaving a junction is counted as negative)

Question 2

What is Kirchhoff’s second law?

Answer 2

The sum of the potential difference across a closed loop is zero.
Or
The sum of the emfs in any closed loop is equivalent to the sum of the potential drops in that loop

Question 3

How do you work out the total resistance of a set of resistors in series?

Answer 3

Rt = R1 +R2+…..

Question 4

How do you work out the total resistance of a set of resistors in parallel?

Answer 4

R = (1/R1 + 1/R2 + 1/R3 + ….)^-1

Question 5

What is the potential divider equation?

Answer 5

Vout = R2/(R1+R2) x Vin

Question 6

Define electromotive force (E.M.F.)

Answer 6

The energy gained per unit charge when passing through a supply (cell).

Question 7

define internal resistance

Answer 7

The internal resistance of a source of e.m.f. is the resistance to electric current of the materials inside a cell.

Question 8

define terminal p.d.

Answer 8

The terminal p.d. is the potential difference recorded across the terminals of a cell. The difference between the e.m.f. and the terminal p.d. when charge flows in the cell is called the ‘lost volts’.

Question 9

What are the lost volts?

Answer 9

The difference between the e.m.f. and the terminal p.d. when charge flows in a cell.

Question 10

What are the Internal resistance equations?

Answer 10

ε = IR + Ir
ε = I(R + r)
ε = V + Ir
ε = e.m.f. (V)
r = internal resistance (Ω)
R = resistance of load in the circuit (Ω)
V = p.d. across the load in the circuit, or, the terminal p.d. (V)

Question 11

What are the gradient and y intercept equal to on a p.d. current graph?

Answer 11

gradient = internal resistance
intercept = e.m.f.