Topic 9 - further electricity

Question 1

Live wire? (2)

Answer 1

• Carries electrical current to the appliances. Electrical current flows in through the live wire
• Alternates between high positive and low negative potential differences

Question 2

Neutral wire? (2)

Answer 2

• Wire are complete the circuit. Electrical current flows out through the neutral wire
• Wire has a potential difference of 0V

Question 3

Earth wire (4)

Answer 3

• For safety, provides pathway for current to flow from a device to ground if the device has a fault
• Why is connected to the metal casing of appliance
• Wire has a low resistance
• If fault, earth wire takes current to the ground

Question 4

Double insulation? (2)

Answer 4

• Improve safety by having a plastic case
• If 1 layer is damaged the appliance is still safe

Question 5

Fuses and circuit breakers? (6)

Answer 5

• If a fault develops (live wire touches metal case), the huge current flows through the live wire through the metal case and then through the earth wire
• The huge current causes the fuse to note of the circuit breaker to trip this cuts off the live supplier of current
• Whole appliances isolated
• Prevents electric shock and fire from heating
• Fuses have to be replaced
• Circuit breaker has to be reseted by flipping a switch

Question 6

Charge, voltage and energy transfered equation?

Answer 6

Energy transfered =

E = qV

Question 7

Resistance, current and energy (3)

Answer 7

• When electric current flows through a resistor, energy is transferred as heat energy
• When electric current flows of electrons collide with the ions in the lattice in the resistor
• Ions vibrate faster which causes the resistor to heat up

Question 8

What happens if the resistor get heated up? (3)

Answer 8

1. Resistance of the resistance increases
2. Less current flow
3. Larger voltage needed to have the same current

Question 9

Heating effects of electrical current dis

Answer 9

Lots of energy lost as heat energy in the circuit

Question 10

Heating effects of electrical current adv

Answer 10

For appliances like toasters, when current is passed through the coil, it temperature increases and it and that’s infrared heat radiation which cooks the bread

Question 11

Electrical power?

Answer 11

Is the rate at which energy is transferred

Question 12

Electrical power equation?

Answer 12

P = E/t

OR

P = VI

Question 13

Current ratings in fuses?

Answer 13

Fuses must have current ratings near but higher than normal operating current

Question 14

Diode? (3)

Answer 14

• Are made of semiconductors
• They conduct current (when a very low resistance) only when connected in One Direction
• They do not conduct current (when has a high resistance) when connected in an opposite direction (partially conduct very little current)

Question 15

LED - Light Emitting diodes: (2)

Answer 15

• They are diodes, so they Willamette light when current flows in the forward bias direction
• No filament inside

Question 16

LRD - Light Dependent Resistor (2)

Answer 16

• Resistance of LDR changes with light intensity incident on it
• Resistance of LDR decreases with increasing brightness

Question 17

Thermistor: (2)

Answer 17

• Resistance of thermistor changes with temperature
• resistance of thermistor decreases with increase in temperature

Question 18

Charge, voltage and energy transfer?

Answer 18

Voltage is the energy transferred per unit charge passed