Internal Resistance

Question 1

Internal Resistance (r)

Answer 1

Resistance within Power Sources
Internal resistance reduces the P.D. available by the power source as charges pass through the source of EMF
Due to work being done by the charges as they move through the power source

Question 2

Lost Volts

Answer 2

Volts taken in due to internal resistance
EMF = Terminal P.D. + Lost Volts

Question 3

Terminal P.D.

Answer 3

P.D. available to the components in the series circuit
Lost Volts = Current x Internal Resistance
If current increases, lost volts increases
If current is 0, there are no lost volts

Question 4

Equation

Answer 4

E = V + Ir or E = I(R + r) -> Current is constant
E: EMF of the power supply
V: Terminal P.D. in volts
I: Current through the power supply in Amperes
R: Circuit Resistance in Ohms
r: Internal Resistance of the power supply in Ohms

Question 5

Connecting Cells

Answer 5

Cells can be connected to produce a higher EMF or higher current, by connecting in series and parallel to produce a desired effect

Question 6

Connecting Cells: Series

Answer 6

Increases EMF, but also increases internal resistance limiting available current

Question 7

Connecting Cells: Parallel

Answer 7

Produces a lower EMF (Same as a single cell)
Will have a much smaller internal resistance, so provides a greater current

Question 8

Investigating Internal Resistance

Answer 8

Record values of terminal p.d. and current
To change the current we alter the resistance of the variable resistor
Plot a graph of terminal p.d., V against current, I

Question 9

Analysis of Internal Resistance

Answer 9

E = V + Ir
V = -Ir + E
y = mx + c
Y-Intercept is EMF
-ve gradient is internal resistance
We can see that as current increases, terminal p.d. decreases
This means that lost volts is increasing
When current is zero, terminal pd = EMF of the cell
Do not let the current get to high: Temperature will increase, internal resistance will increase