Emf, Internal resistance and circuit diagrams

Question 1

The internal resistance of a source of electricity is due:

Answer 1

To opposition to the flow of charge for the source. This causes electrical energy produced by the source to be dissipated inside the source when charge flows through it.

Question 2

Define internal resistance.

Answer 2

The internal resistance of a source is the loss of pd per unit current in the source when current passes through the source.

Question 3

Define terminal pd

Answer 3

• The electrical energy per unit charge delivered by the source when it is in the circuit.
• The terminal pd is less than the emf whenever current passes through the source. The difference is due to the internal resistance.

Question 4

The electromotive force of the source is:

Answer 4

the electrical energy per unit charge produced by the source

Question 5

ε =

Answer 5

E/Q

Question 6

Cell current =

Answer 6

ε/R+r

Question 7

cell emf

Answer 7

I(R + r) = IR + Ir = terminal pd + lost pd

Question 8

Power supplied by the cell

Answer 8

Iε = I²R + I²r = power delivered to R = power wasted in the cell due to internal restance.

Question 9

When a source delivers power to a load:

Answer 9

Maximum power is delivered to the load when the load resistance is equal to the internal resistance of the source.

Question 10

Measuring terminal pd.

Answer 10

• Connect a high resistance voltmeter directly across the terminals of the cell.
• The current is changed by adjusting the variable resistor. The lamp or a fixed resistor limits the maximum current that can pass through the cell.
• An ammeter measures the current.

Question 11

Why does the terminal pd decrease as the current increases.

Answer 11

• This is because the lost pd increases as the current increases.
• The terminal pd is equal to the cell emf at zero current. This is because the lost pd is 0V is 0A.

Question 12

r when 2 terminal pds are known

Answer 12

r = (V₁-V₂)/(I₂-I₁)