chapter 13 electrical systems

Question 1

what is electric currents? and how is it measured?

Answer 1

• the rate of flow of electric charge

- it is measured by the amount of electric charge moving per unit time past any point in the circuit

Question 2

what is the SI unit for current?

Answer 2

• Ampere (A)

- one ampere of current means that one unit of charge flows per second

Question 3

what current flows from a positive terminal of a battery to a negative terminal of a battery? and what current moves from a negative terminal to a positive terminal?

Answer 3

• conventional current

- electron flow

Question 4

name the function of these things in a circuit:

1. switch
2. energy source
3. wires
4. bulb

Answer 4

1. it turns the current on or off
2. provides energy for the current to flow in a circuit
3. connects the components together and provides a path for the current to flow
4. converts electrical energy into light and heat

Question 5

what is a series circuit?

Answer 5

when the components are joined one after another in a single loop
- electrical current passes through one single path

Question 6

what is a parallel circuit?

Answer 6

• electric current is divided into branches
• electrical components are connected in each branch
• electric current will pass through all the branches

Question 7

what is potential difference?

Answer 7

• the p.d of any two points is the amount of energy needed to move one unit of electric charge from one point to another

Question 8

What is the SI unit of potential difference?

Answer 8

• volts (V)
• one volt of potential difference means that you need one joule of energy is needed to move one unit of electrical charge

Question 9

what is resistance?

Answer 9

• the resistance of a component is the ratio of potential difference across it to the current flowing through it
• the electrical component resists or hinders the flow of electric charges when it is connected in a circuit

Question 10

what are variable resistors?

Answer 10

• rheostat
• a resistor whose resistance can be adjusted easily
• when slider is on the left- short resistance
• when sliders is on the right - long resistance

Question 11

what are the effects of electric current?

Answer 11

• magnetic effect
• chemical effect
• heating effect
• lighting effect

Question 12

what are the chemical effects of electric current?

Answer 12

extraction of metal ( electrolysis):

• electricity can be used to break down compounds into its elements
  eg. aluminum can be extracted from bauxite

electroplating:
-coating objects with metal by immersing the object in a liquid and then passing an electric current through the liquid

Question 13

what is the magnetic effect of electric current?

Answer 13

electromagnets:
- magnetic effect by making current flow in a coil of wire (solenoid)
- an iron rod can be placed inside which will turn the iron rod into an electromagnet

Question 14

what is the heating effect of an electric current?

Answer 14

-electrical energy passes through a wire and is converted to heat energy
> heating elements are made of materials with high melting points like
>nichrome, iron, Nickle and chromium

Question 15

what is the lighting effect of an electric current?

Answer 15

• in a light bulb, the current causes the filament to heat up and therefore glows and gives out light

Question 16

what is power?

Answer 16

the power of a circuit component is the amount of electrical energy converted to other forms of energy per unit time by the component

Question 17

What is the SI unit of power?

Answer 17

• watt (W)

- one watt of power means that in one second, one joule of energy is converted to other forms

Question 18

what does the power rating of an appliance tell us?

Answer 18

• how quickly an electrical appliance converts electrical energy to other forms of energy

Question 19

what is the unit for power and what is the unit for energy?

Answer 19

power: watt (W)
energy: Joule (J)

Question 20

What is the formula for energy?

Answer 20

energy = power x time

j or kWh = w x h

Question 21

What are the three wires in an electrical appliance?

Answer 21

Earth wire: (yellow and green) connected to the ground on earth: it provides a path of low electrical resistance, the large current flows directly into the ground

live wire: (brown)
neutral wire

Question 22

what is a fuse and what does it do?

Answer 22

• a short thin wire
• it makes use of the heating effect of an electric current to switch off a large current
• a large current causes the shorth thin wire in the fuse to heat up and melt
• a fuse is connected to a live wire
  > is rated with the current that will melt the wire in it
• if the fuse melts, it has ‘blown’
  > needs to replace after an electrical fault

Question 23

what is a circuit breaker?

Answer 23

• it cuts off electric current but does not need to be replaced
• found in a box called consumer unit
• the main switch turn off or on all electricity in the household
• when the current in one part is too large, usually only the circuit breaker for that part turns off ‘trips’

Question 24

what are heating elements made of?

Answer 24

• nichrome

an alloy of chronium, nickle and iron