3.5.1.6 Electromotive force and internal resistance

Question 1

What is the electromotive force?

Answer 1

The amount of chemical energy converted to electrical energy per coulomb of charge (C) when passing through a power supply

Question 2

How can emf be measured?

Answer 2

By connecting a voltmeter connected in parallel with the cell, or connecting a high-resistance voltmeter around the terminals of the cell in an open circuit

Question 3

What is terminal potential difference?

Answer 3

The p.d. across the terminals of a cell. If there was no internal resistance, terminal p.d. would be equal to e.m.f.

Question 4

What is the equation for terminal p.d.?

Answer 4

V=IR

Question 5

What are lost volts?

Answer 5

The work done per unit charge/ coulomb to overcome the internal resistance/ resistance inside the battery when current flows
- it is the voltage lost in the cell due to internal resistance
from the conservation of energy,
v = emf - terminal p.d. = Ir

Question 6

What is internal resistance?

Answer 6

The internal resistance of a source is the lose of p.d. per unit current in the source when charge passee through the source
-it is the electrical resistance within any cell, battery or power supply

Question 7

Why does the cell become warm after a period of time?

Answer 7

It is the internal resistance that causes charge circulating to dissipate some electrical energy from the power supply itself, and over time it can cause loss of voltage or loss of energy in a power supply.