Effects Of An Electric Current And Domestic Circuits

Question 1

Joule’s law

Answer 1

Joule’s law states that the rate at which heat is produced in a conductor is directly proportional to the square of the current provided its resistance is constant

Question 2

Transformers

Answer 2

Are devices that can change the voltage of the supply.

Since power = current x voltage, i.e. P=IV, the bigger the voltage the smaller the current for a given power

Question 3

Electrolyte

Answer 3

The liquid in which the chemical reaction (electrolysis) takes place

Question 4

Electrolysis

Answer 4

When an electric current causes a chemical reaction when it passes through a liquid

Question 5

Electrodes

Answer 5

The rods or plates that dip into the electrolyte

Electrolysis

Question 6

Anode

Answer 6

The electrode connected to the positive of the power supply (electrolysis)

Question 7

Cathode

Answer 7

The electrode connected to the negative of the power supply (electrolysis)

Question 8

Voltametre

Answer 8

The container, electrolyte and electrodes together are called the voltametre (electrolysis)

Question 9

Inactive electrodes

Answer 9

If the electrodes do not take part in the chemical reaction (electrolysis)

Question 10

Active electrodes

Answer 10

If the electrodes do take part in the chemical reaction (electrolysis)

Question 11

Examples of electrolytes

Answer 11

• a solution of an acid, base or salt in water

- an ionic compound in its molten state

Question 12

Ion

Answer 12

An atom or a molecule that has lost or gained one or more electrons is called an ion

Question 13

Charge carriers in an electrolyte

Answer 13

In an electrolyte the charge carriers are positive and negative ions

Question 14

The electrolysis of water

Answer 14

Breaking water up into hydrogen and oxygen by passing an electric current through it

Question 15

Applications of the chemical effect of an electric current

Answer 15

• electroplating
• extracting metals from their ores
• purifying metals
• electrolytic capacitors

Question 16

Electroplating

Answer 16

Covering one metal with a thin layer of another, usually to protect the first one from corrosion and make it look better. The metal object to be electroplated must be cathode

Question 17

Relationship between current and voltage for different conductors: a metallic conductor

Answer 17

• the voltage and the current are directly proportional (ohms law)
• in a metal the charge carriers are negative electrons

Question 18

Relationship between current and voltage for different conductors: a filament bulb

Answer 18

• as the voltage across a filament bulb is increased, the current increases. As it does so, the filament gets significantly hotter and its resistance increases. Thus, when the filament is hot, a given increase in V does not produce as much of an increase in I as when it is cooler. The I-V graph thus becomes less steep
• in a filament bulb the charge carriers are negative electrons

Question 19

Relationship between current and voltage for different conductors: a semiconductor e.g a thermistor

Answer 19

• as the voltage across a semiconductor is increased, the current increases. As it does so, the semiconductor gets hotter. This produces many more holes and electrons which are available for conduction and its resistance drops. A further increase in V produces a much larger increase in I than when it was cold. The I-V graph thus gets much steeper.
• in a semiconductor the charge carriers are negative electrons and positive holes

Question 20

Relationship between current and voltage for different conductors: ionic solutions i.e. electrolytes

Answer 20

• as the voltage increases so does the current. The resistance remains constant and thus the I/V graph is a straight line
• in an electrolyte the charge carriers are positive ions and negative ions

Question 21

Relationship between current and voltage for different conductors: a gas

Answer 21

In a gas, the charge carriers are positive ions, negative electrons and a few negative ions

Question 22

Examples of gas discharge tubes

Answer 22

• sodium vapor lamp
• sodium vapor street lamps (yellow/orange)
• neon lamps

Question 23

Distribution box

Answer 23

Where the live and neutral wires pass through upon entering the house (after passing the meter).

Question 24

Radial circuit

Answer 24

Circuits with a separate live and neutral wire coming from the distribution box.
Used for appliances that take a large current
Each radial circuit has its own fuse

Question 25

Ring circuit

Answer 25

In a ring circuit the live terminals of each socket are connected together. The neutrals are also connected together, which is then connected back to the neutral at the distribution box
Each ring circuit has a fuse in its live

Question 26

Switches

Answer 26

A switch should always be connected in the live wire

Question 27

Fuse

Answer 27

A fuse is a piece of wire that will melt when a current of certain size passes through it
- a fuse should be connected in the live wire

Question 28

Miniature circuit breakers (MCBs)

Answer 28

Are usually used instead of fuses in the distribution box

They contain a bimetallic strip and an electromagnet

Question 29

Residual current devices (RCDs)

Answer 29

The circuits connected to the sockets in a house are protected by residual current devices. They operate by detecting a difference between the current in the live and the neutral which could arise if someone comes in contact with the live and current flows through them to earth

Question 30

Plugs: the wire colours

Answer 30

Live = brown 
Neutral = blue
Earth = green/yellow

Question 31

Kilowatt-hour

Answer 31

The kilowatt-hour (kWh) is the amount of energy used by a 1000 W appliance in one hour