Chapter 12 - Electric Current

Question 1

Current

Answer 1

The rate of flow of charge

Question 2

Potential difference

Answer 2

Energy transferred (work) from each coulomb of charge

Question 3

emf

Answer 3

Energy transferred (work) to each coulomb of charge

Question 4

Resistance of an ideal voltmeter

Answer 4

Infinite

Question 5

Resistance of an ideal ammeter

Answer 5

Zero

Question 6

Resistance

Answer 6

Opposition to the how of charge, ohms

Question 7

Ohmic conductor

Answer 7

Pd is proportional to current if temperature is constant

Question 8

Diodes

Answer 8

Only allow current to flow in one direction

Question 9

Filament lamp

Answer 9

Resistance increases as temperature increases

Question 10

Thermistors

Answer 10

Resistance decreases as temperature increases

Question 11

Why does a conductors resistance increase as temp increases?

Answer 11

The positive ions in the conductor vibrate more when its temp is increased. The conduction electrons therefore cannot pass through the metal as easily. This is a positive temperature coefficient because its resistance increases with increase of temperature

Question 12

Why does a semiconductors resistance decrease as temperature increases?

Answer 12

The number of conduction electrons increases when the temperature is increased. A thermistor made from an intrinsic semiconductor therefore has a negative temperature coefficient

Question 13

Superconductors

Answer 13

Have zero resistiviry below a certain temperature

Question 14

Critical temperature

Answer 14

Temperature below which the resistivity of a superconductive material is zero

Question 15

Uses of superconductors

Answer 15

Produces large magnetic fields
Transmission of electricity

Question 16

Charge carriers in metals and non-metals

Answer 16

Metals - charge carriers are conduction electrons. They repeatedly collide with each other and the fixed positive ions in the metal
Salt solution - charge carried by ions

Question 17

Insulator

Answer 17

Each electron is attached to an atom and cannot move away from the atom. When a voltage is applied across an insulator, no current passes through the insulator, because no electrons can move through the insulator

Question 18

Conductor

Answer 18

Most electrons are attached to atoms but some are delocalised - the delocalised electrons are the charge carriers in the metal. When a voltage is applied across the metal, these conduction electrons are attracted towards the positive terminal of the metal

Question 19

Semiconductor

Answer 19

The number of charge carriers increases with an increase of temperature. The resistance of a semiconductor therefore decreases as its temperature is raised

Question 20

Equation for power

Answer 20

Power = potential difference x current
Power = energy / time

Question 21

Ohm’s law

Answer 21

That the pd across a metallic conductor is proportional to the current through it, provided the physical conditions do not change

Question 22

Unit of resistivity

Answer 22

Ohm metre

Question 23

W

Answer 23

Work done, joules

Question 24

Work done

Answer 24

• energy transferred
• energy lost from a store
• energy changed between stores

Question 25

What effects the resistance of a component?

Answer 25

• length
• cross sectional area
• material
• temperature

Question 26

Resistivity equation with length as the subject

Answer 26

Length = (resistance x area) / resistivity

Question 27

Resistivity equation with resistance the subject

Answer 27

Resistance = (resistivity x length) / area

Question 28

Cross-sectional area

Answer 28

Pi x r^2

Question 29

How does the resistance of a lamp vary as the voltage is increased from zero to its working voltage

Answer 29

The resistance of he lamp increases with the voltage. Resistance and voltage are directly proportional to each other. The resistance increases as the filament lamp gets hotter because the positive ions are vibrating more which makes it more difficult for the charge carrying electrons to get through as there are more collisions of the electrons with the lattice ions.

Question 30

What’s the significance of the critical temperature of a material?

Answer 30

Below the critical temperature the material has no resistance and thus no potential difference

Question 31

The resistance of a metallic conductor increases with temperature because, at higher temperatures

Answer 31

The amplitude of vibration of lattice ions increases