Effect of an Electric current and domestic current

Question 1

Heating effect

Answer 1

The amount of heat produced by an electric current is dependent on the size of the current, the resistance of the conductor and the time for which it flows through

Question 2

Joule’s Law

Answer 2

The rate at which heat is being produced in a conductor is directly proportional to the square of the current provided the resistant is a constant
P=I2R

Question 3

Advantages of using high voltage in transmission of electrical energy

Answer 3

Higher the current the more energy that is dissipated as P=I2R. Larger current the larger the energy lost

Question 4

Chemical effect

Answer 4

Electric current may cause a chemical reaction when passes through a liquid

Question 5

Application of chemical effect

Answer 5

Electroplating - covering one metal with another layer of metal
Extracting metals from their ore
Purifying metals
Manufacture of one particular type of electrolytic capacitor

Question 6

Metallic conductors

Answer 6

Provide the temperature remains constant as the voltage increases the current increases directly proportionally
In a metal the charge carrier are negative electrons

Question 7

Filament lightbulb

Answer 7

Voltage increases the current increases
Higher current flowing there is temperature rise as the wire hearts and resistance increases
When filament is hot there is not the same charge in current for an increase in voltage
Charge carriers are the negative electrons

Question 8

Semiconductors (thermistors)

Answer 8

Voltage increases there is an increase in current
This increase in current causes a temperature rise
This temperature rise causes more hole and conducting electrons to be released reducing the resistance
A further increase in voltage results in a much larger increase in current
Charge carriers are negative electrons and positive hole

Question 9

Ionic solutions - electrolyte

Answer 9

As the p.d. increases the current also increases, the resistance remains constant thus you get a straight line graph
If electrodes are active they obey Ohm’s Law and pass through the origin
If electrodes are inactive the voltmeter behaves as a cell and produces an emf across the plate, the applied voltage must be larger than this emf before the current will flow

Question 10

Gas

Answer 10

• A discharge tube has gas at low pressure.
• Due to backgroung radiation and cosmic
  rays there will always be some ions being
  formed in the gas.
• These ions recombine with their electrons
  after a while.
• If a p.d. is applied across the tube, the
  positive ions move towards the negative
  plate and the electrons towards the
  positive plate and a current flows.
  As the p.d increases the number of ions crossing
  the tube increases as so does the current
• At a certain p.d. all the ions produced cross the
  tube before recombining so s further increase in
  p.d. produces no further increase in current.
• As the p.d. is increased a stage is reached
  where the ions and electrons have enough speed
  to produce other ions and electrons by collisions
  with a result the current increases with voltage.
• In a gas the charge carries are the positive ions
  and the negative electrons

Question 11

Vacuum

Answer 11

A vacuum will not conduct electricity as there
are no charge carriers.
* However if the cathodeis heated enough
thermionic emissions will occur (electrons
from a hot metal)
* Electrons gain enough energy to to leave the
cathode and as the p.d. increases the current
increases until all electrons emitted are
carried across the tube, any further increase
will cause no further increase in current

Question 12

Domestic current

Answer 12

• The domestic circuits have the
  current that enter divided into
  different circuits to prevent excess
  current from flowing through.
• A distribution box is used to separate
  out the current.
• Any device such as electric cooker or
  electric shower is connected in such
  a way that they are all on their own
  fuse called a radial circuit.

Question 13

Lighting current

Answer 13

• Lights don’t take much current
  so many lights can be
  connected together.
• Each light is connected in
  parallel so that if one bulb blows
  the other bulbs will stay
  working.

Question 14

Ring current

Answer 14

• In the ring circuit the live wire
  of each of the plugs is
  connected together and the
  neutral wire are connected
  together.

Question 15

Switches and fuses

Answer 15

• Both the switch and fuse should
  be located on the live wire to
  prevent electrocution.
• A fuse is a piece of wire with a
  low melting point, when too
  much electricity flows through
  it.

Question 16

Miniature circuit breaker

Answer 16

• Miniature Circuit Breakers (MCBs) are
  now used instead of fuses in
  distribution boxes.
• They contain a bimetallic strip and an
  electromagnet.
• The bimetallic strip causes the
  contacts to pull apart for small
  current.
• The electromagnet is used for larger
  currents.
• They operate faster than fuses and
  can be reset by flicking the switch

Question 17

Residual current devices

Answer 17

• The sockets in houses are also
  connected to RCDs.
• They operate by detecting a
  difference between the current
  between the live and the neutral
  wire. (if there was a short circuit
  somewhere)
• The RCDs trips very quickly
  disconnecting the circuit from the
  live.

Question 18

Bonding

Answer 18

• Bonding is a safety system where all
  metals taps, pipes, water tanks, etc.
  are connected to earth.
• If the pipe was to come in contact
  with the live wire they will remain at
  0V and will not pose the risk of
  electrocution.

Question 19

Earthing

Answer 19

• Earthing is a safety feature where if
  the live wire comes in contact with
  metal outer of an object, there is a
  risk of electrocution.
• If it is earthed the current from the
  live wire passes through the earth,
  due to the low resistance excess
  current will flow blowing the fuse