1. A cell of negligible internal resistance is connected in series with two resistors of 100Ω and 200Ω.
The current through the resistors is 300mA.
Calculate the terminal p.d. of the cell.
What is the e.m.f. of the cell?
1. The p.d. across the terminals = the p.d. across the external resistors
V=IR
V = 300 x 10-3 x 300
V= 900 x 10-3
V = 90.0V
Always draw the arrangement V
2. The question tells us that the internal resistance of the cell is negligible.
When this is the case
The e.m.f. = terminal p.d.
E = 90.0V
I= 300 x 10-3A
100Ω
200Ω V

2. The resistance of this meter is negligible
The terminal potential of an unconnected cell is 1.51V.
The cell is connected in series with a 10kΩ and a microammeter of negligible resistance. The p.d. across the resistance is measured as 1.49 volts by a high resistance voltmeter.
Calculate the internal resistance of the cell:
The terminal potential of the unconnected cell is the e.m.f. of the cell
10kΩ μA r
The current through the series circuit is the same everywhere
The resistance of this meter is negligible
1.49V

3. E = 1.51 V r μA 10kΩ Applying the formula for internal resistance:

4. V A R1 R2
A cell is connected to a switch and two resistors R1 and R2 with values of 100Ω and 400Ω which are in parallel. When the switch S is open, the high resistance voltmeter V reads 1.63V.
When switch S is closed V reads 1.61V.
1.Calculate the current registered by the ammeter A assuming that it has negligible resistance.
2. Calculate the internal resistance of the cell

5. A cell is connected to a switch and two resistors R1 and R2 with values of 100Ω and 400Ω which are in parallel. When the switch S is open, the high resistance voltmeter V reads 1.63V.
When switch S is closed V reads 1.61V.
1.Calculate the current registered by the ammeter A assuming that it has negligible resistance.
The value of the resistance in the circuit is given by
The current though the “series” circuit
I = 0.02A

6. 2. Calculate the internal resistance of the cell
ε=1.63V .
I = 0.02A
1.63 = 0.02x r
r = ( )/0.02 V A R1 R2