Electrical systems (13)

Question 1

What are the useful effects of electricity?

Answer 1

Chemical
Heating
Magnetic

Question 2

What are the harmful uses of electricity?

Answer 2

Electric shocks
Electrical fires

Question 3

What are some safety devices?

Answer 3

Fuses and circuit breaker

Question 4

What are the main components of a circuit and what are their uses?

Answer 4

Cells ( batteries ): used to provide energy (chem to electrical)
Electric charges: carries electrical energy from cell to devices
Wires: path for electric charge to flow
Electrical devices used to convert electrical energy to other forms, e.g
- Bulb: electrical to light energy
- Resistor: electrical to heat energy

Question 5

What is electric current, I? (meaning)

Answer 5

It is the rate of flow of electric charges in Ampere (A) (unit)

Question 6

What is potential difference,V? (meaning)

Answer 6

It is the amount of energy needed to move a unit charge from one point to another point in volt, (V)

Question 7

Where are ammeters and voltmeters placed in a circuit?

Answer 7

Ammeters needs to be connected in series. ( can be anywhere in series )
Voltmeter needs to be connected in parallel to the bulb.

Question 8

What is electrical resistance?

Answer 8

It is how much a component, e.g resistor, opposes the flow of electric current in ohms (unit)

Question 9

What are some electrical conductors.
Which has low or high resistance?

Answer 9

Electrical conductors
- Low resistance: copper, silver
- High resistance: tungsten, nichrome

Question 10

What happens when resistors are placed in series in a circuit?

Answer 10

• The bulb is dimmer
• There is only one path for the current to flow
• Overall resistance increases
• Current through the circuit decreases

Question 11

What happens when resistors are placed in parallel in a circuit?

Answer 11

• The bulb is brighter
• More than one path for current to flow
• Overall resistance decreases
• Current flowing through the circuit increases

Question 12

What is power and its unit?

Answer 12

Watt (W)
It is the amount of electrical energy used for conversion to other forms of energy per unit time.

Question 13

How do you find the cost of electrical energy?

Answer 13

1) Convert power(w) to kilowatt (kw)
e.g: 1.5W x 1000 = 1500 Kw

2) Calculate energy ( kWh ) using
power (W) x time(h) = energy (kWh)

3) Find cost
energy(kWh) x rate
note that the rate will always be 3 d.p

Question 14

Why can’t ammeters be connected in parallel?

Answer 14

The total currents divide into two parts as there are different pathways
More current goes towards ammeters because it has lower resistance
(meaning that current will go to paths will no/less resistance)

Question 15

How do you conserve energy?

Answer 15

Switch off water heater after use
Buy electrical appliances that have energy labels with three or more ticks.

Question 16

in order to maintain the same brightness of the bulb, suggest how the rheostat should be adjusted.

Answer 16

To increase resistance, the slider of the rheostat should be adjusted to the right.

To decrease resistance, the slider should be adjusted to the left.