Chapter 13
Electrical systems
electrical components
wires
cell/battery
switch
bulb
harmful effects
electrical fire
- when multiple plugs are inserted into the same socket, large amounts of energy is drawn from the power supply. this results in excessive heat and may cause an electrical fire.
electric shock
- if a person gets into contact with an exposed wire, the electric current flows through the body and results in an electric shock.
safety measures to prevent electricity from harming yourself and others
- do not overload power sockets
- change/replace worn out wires with new ones
- do not touch electrical appliances with wet hands
- do not insert objects into the opening of a socket
ways to conserve energy
- buy appliances that have energy labels with three or more ticks
- switch off water heater after use
- switch off lights and fans when not in use
- switch off air conditioner after a short while before switching to a fan
power
ammeter
the amount of electrical energy used for conversion to other forms of energy per unit time
calculating energy (kWh)
Energy (kWh) = Power (kW) x Time (hours)
calculating cost ($)
Cost ($) = Energy (kWh) x Time (cost per kWh)
Q: You have a household appliance with a power consumption of 1500 watts. It was used continuously for 5 hours. If the cost of electricity is $0.12 per kilowatt-hour, what is the total cost of using the appliance?
A: find the kW (kilowatt) by converting W (watt) into kW.
1000W = 1kW,
so 1500W = 1.5kW
substitute the values into the formula for finding kWh
- kW x time (in hours, convert according if Q gives u minutes) = kWh
- 1.5 x 5 = 7.5kWh
- 1.5 x 5 = 7.5kWh
substitute the values into the formula for finding cost
- energy (kWh) x cost per kWh = cost ($)
- 7.5kWh x $0.12/kWh = $0.9 (cost) ✓
⏫ remember to write down two decimal place as value is in $
conversion (W to kW)
1,000W = 1 kW
measures current flowing through an electric circuit
SI Unit: ampere (A)
circuit symbol
voltmeter
- measures potential difference (amount of energy needed to move a unit charge from one point to another in a circuit) across an electrical component
- connected in parallel with the circuit
circuit symbol:
resistors
opposes the electrical current, which is known as electrical resistance (R)
higher resistance → decreases flow of current
lower resistance → increase flow of current
SI Unit: ohm (Ω)
types of resistors
fixed resistor (fixed, non-adjustable electrical resistance)
circuit symbol:
variable resistor (has a range of electrical resistance, adjustable)
circuit symbol:
series arrangement
current decreases as resistance increases as there is only one pathway for current to flow through, thus overall current is higher
parallel arrangement
current increases as resistance decreases due to more currents, allowing the current to flow through multiple pathways
SI Unit: volt (V)