P4.3 Electrical circuits and P4.4 Electrical safety

Question 1

Definition of cells / batteries / power supplies

Answer 1

A device that provides an e.m.f in a circuit by means of chemical reaction.

Question 2

Definition of switches

Answer 2

A circuit component that allows or blocks the flow of electrical current

Question 3

Definition of resistors (fixed and variable)

Answer 3

A component in an electric circuit that decreases the current
- Fixed resistors have a constant value so resistance provided by it is constant.
- Variable resistor is an electrical component whose resistance can be changed manually

Question 4

Definition of heaters

Answer 4

A device in an electric circuit for the conversion of electric energy into heat.

Question 5

Definition of lamps

Answer 5

A component in an electric circuit that is used to provide illumination.

Question 6

Definition of motors

Answer 6

A coil of wire carrying a current in a magnetic field, experiences a force that tends to make it rotate.

Question 7

Definition of fuses

Answer 7

A device that breaks the circuit if the current exceeds a certain value; it is a piece of metal wire that melts when too much current flows through it.

Question 8

Definition of generators

Answer 8

Devices that turn mechanical energy into electrical energy

Question 9

Definition of light-emitting diodes (LEDs)

Answer 9

A type of diode that illuminate when placed in the correct direction when a current flows in a circuit.

Question 10

Current in series vs current in parallel

Answer 10

• Current at every point in a series circuit is the same
• Current is shared between different junctions in parallel

Question 11

Potential difference in series vs potential difference in parallel

Answer 11

• Potential difference is shared between different components in a series circuit.
• Potential difference at every point in a parallel circuit is the same

Question 12

Resistance in series vs resistance in parallel

Answer 12

• Total resistance in series is the combined resistance of two or more resistors
• The combined resistance of two resistors in parallel is less than that of either resistor by itself

Question 13

Equation for resistors in series - combined resistance

Answer 13

R = R1 + R2 + R3 … + Rn R: Total resistance; R1: First resistor in series; R2: second resistor in series

Question 14

Equation for resistors in parallel - combined resistance

Answer 14

1/R = 1/R1 + 1/R2 + … + 1/Rn R: total resistance; R1: First resistor in series; R2: second resistor in series

Question 15

Equation to find voltage across only 1 component in series circuit

Answer 15

Vout = Vin x (R/Rt) Vout: potential difference across component (volt); Vin: input potential difference (volt); R: resistance of component and Rt is the total resistance (Ohm)

Question 16

Describe the heating effect of current

Answer 16

A reference to the phenomenon where electric current flowing through a conductor produces heat. As electrons move through the conductor, they collide with atoms and other particles in the material, transferring some of their energy in the form of heat.

Question 17

State the hazards of damaged insulation

Answer 17

If someone touches an exposed piece of wire, they could be subjected to a lethal shock

Question 18

State the hazards of overheating cables

Answer 18

Passing too much current through a small wire can lead to the wire overheating. This could cause a fire or melt the insulations, exposing live wires.

Question 19

State the hazards of damp conditions

Answer 19

If moistures come into contact with live wires, the moisture could conduct electricity either causing a short circuit within a device leading to fire, or posing a risk of electrocution.

Question 20

State the hazards of overload of plugs

Answer 20

If plugs or sockets become overloaded due to plugging in too many components the heat created can cause fires
=> Plugging in multiple adaptors to another multiple adaptors should be avoided

Question 21

Explain the use of fuses and trip switches

Answer 21

• A fuse is a thin piece of wire which overheats and melts if the current is too high, when the fuse melts and breaks the circuit, the components are protected from damage.
• When the current flows through a switch exceeds a certain value, the trip switch will switch off and break the circuit; this can replace the fuse

Question 22

Explain why outer casing of an electrical appliance must be either non-conducting (double insulated) or earth

Answer 22

• Must be non conducting so that there are 2 layers of electrically insulating material so the electric current can not pass through, even if a live wire touched the casing due to wiring damage.
• Must be earth to deliver the excess current in the metal case maybe from faulty wiring touching it through the Earth wire and down to the Earth => metal case no longer has excess current => Safety