6.8 EMF and Internal Resistance

Question 1

What is internal resistance?

Answer 1

Resistance comes from electrons colliding with atoms and losing energy. In a battery, chemical energy is used to make electrons move. As they move, they collide with atoms inside the battery.

Question 2

What is load resistance?

Answer 2

The total resistance of all the components in the external circuit

Question 3

What is e.m.f?

Answer 3

The amount of electrical energy the battery produces and transfers to each coulomb of charge.

Question 4

What is terminal p.d?

Answer 4

The potential difference across the load resistance (the energy transferred when one coulomb of charge flows through the load resistance)

Question 5

What are the lost volts?

Answer 5

The energy wasted per coulomb overcoming the internal resistance

Question 6

What is the equation for emf? (Energy and charge)

Answer 6

EMF = energy/charge

Question 7

What is the equation for emf and internal resistance?

Answer 7

EMF = current x (load resistance + internal resistance)

Question 8

How can you measure the internal resistance and emf of a cell or battery?

Answer 8

1. Set up a circuit with a cell/battery, ammeter, voltmeter and variable resistor
2. Set the variable resistor to its highest resistance. Record the current through and potential difference across the circuit. Repeat to get a set of results and average.
3. Decrease the resistance of the variable resistor by a small amount and repeat.
4. Repeat unit you have a set of mean currents and potential differences for 10 different load resistances
5. Plot a V-I graph for your data and draw a line of best fit
6. Make sure all other variables are kept constant when carrying out the experiment, including external factors like temperature.
7. From the graph, the y-intercept is the emf and the gradient is -r