Electricity DONE

Question 1

What is potential difference?

Answer 1

Potential difference is the work done per unit charge (energy required to move one Coulomb of charge through a component)

Question 2

What is resistivity?

Answer 2

Resistivity is the resistance of 1 metre of the material with a cross-sectional area of 1 m^2

Question 3

What is Ohm’s law for an ohmic conductor and the condition it relies on?

Answer 3

Ohm’s law states that the current through an ohmic conductor is directly proportional to the p.d. across it
Provided temperature is constant

Question 4

Different materials have different numbers of charge carriers. Compare how metals, semiconductors and insulators differ in terms of current and charge carriers.

Answer 4

Metals- large number of charge carriers from atoms’ delocalised electrons. High current

Semiconductors- fewer charge carriers so smaller current

Insulators- ideally no charge carriers so no current

Question 5

What is total emf equal to?

Answer 5

The total emf around a series circuit= the sum of the p.d.s across each component

It is energy transferred to a unit charge

Question 6

What is meant by power ( in terms of work done) ?

Answer 6

Work done per unit charge per second (P=VI)

Question 7

Explain the I-V characteristic for a filament lamp.

Answer 7

Initially resistance is constant and I is directly proportional to V

As the current increases, the temperature of the filament increases so resistance increases

Thus gradient of the curve becomes shallower as resistance increases

Question 8

Describe the I-V characteristic for an NTC thermistor.

Answer 8

As voltage increases, current increases

Increased current causes an increase in temperature

This means resistance decreases because NTC thermistors decrease in resistance with temperature so gradient of graph increases

Question 9

Explain why the resistance of the LDR decreases with light intensity and how this affects the gradient of the I-V.

Answer 9

Increased light intensity gives electrons more energy to escape from their atoms

This means the number of charge carriers increases so current increases

Thus resistance decreases and gradient of I-V increases

Question 10

Explain what is meant by the internal resistance of a battery, what happens to the battery because of the resistance and state what is meant by load resistance.

Answer 10

Chemical energy makes electrons move. When they collide with atoms/ ions the electrons transfer some of their kinetic energy to other forms. This is internal resistance.

Internal resistance makes batteries warm up when they are used. Load resistance is the total resistance of all the components in the external circuit