ELECTRIC CIRCUITSAug 03, 2018 · Components of a circuit ... Light bulb Ammeter Voltmeter...
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ELECTRIC CIRCUITS - Sutherland High School- Grade 11 Physical Science
Transcript of ELECTRIC CIRCUITSAug 03, 2018 · Components of a circuit ... Light bulb Ammeter Voltmeter...
ELECTRIC CIRCUITS- Sutherland High School-
Grade 11
Physical Science
What you should know already…
1 3
2 4
CURRENT ELECTRICITYMoving charge carried by moving electrons in a wire.
Components of a circuit
Conducting wire SwitchResistors CellLight bulb AmmeterVoltmeter
CONNECTIONS
SeriesParallel
CIRCUITS
A path in which charges
continually move through
a complete loop, returning
to their original position
and cycling through
again.
Closed Open TB. Pg. 265
Electricity Equations
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TB. Pg. 265-267
The difference between EMF and potential difference
• The voltage measured across the terminals of a battery when
NO CURRENT is flowing through the battery is called EMF. The
total amount of energy that a battery can supply.
• The voltage measured across the terminals of a battery when
CURRENT IS FLOWING is called terminal potential difference.
• EMF and potential difference are both measured in volts. (V)
TB. Pg. 267
OHM’S LAWRESISTANCE
The potential
difference over a
resistor is directly
proportional to the
current flowing through
the resistor, provided
the temperature of the
resistor remains
constant.
TB. Pg. 268
Power is the rate of electrical energy conversion in a circuit.
Power is the rate at which energy is provided.
Power
𝑃 = 𝑉𝐼 𝑃 = 𝐼2𝑅𝑃 =
𝑉2
𝑅
𝑃 =∆𝐸
∆𝑡 W= ∆𝐸 Energy conversion - Joules
Pg. 280
A light bulb is marked 220V. 60W.
This means that when the light bulb is connected to a 220V power supply, it radiates 60J of energy every
second in the form of light and heat.
You will need a:
stukkie papier
potlood
sakrekenaar
Divide and conquer
In a series circuit: The greater the resistance, the greater the power.𝑃 ∝ 𝑅
In a parallel circuit, the greater the resistance, the smaller the power.
𝑃 ∝1
𝑅
Brightness of lightbulbs is actually dependant on the power output (voltage x current).
Not just resistance, current or voltage.
New discovery!
Cost calculations
• Power is the rate at which energy is transferred.
• Power is measured in watts.
• 1Watt = 1Joule per second.
• 𝐸𝑛𝑒𝑟𝑔𝑦 𝑡𝑟𝑎𝑛𝑠𝑓𝑒𝑟 = 𝑝𝑜𝑤𝑒𝑟 × 𝑡𝑖𝑚𝑒kilowatt hour
Cost calculations
• It costs Eskom money to provide electrical energy (and to pay for
bonuses and exaggerated salaries). This is why electricity is sold.
• An electric meter measures the energy usage.
• Consumers pay for energy usage – not power or current.
• The consumer pays for the number of kilowatts used and the
time over which it has been used.𝐸𝑛𝑒𝑟𝑔𝑦 𝑡𝑟𝑎𝑛𝑠𝑓𝑒𝑟 = 𝑝𝑜𝑤𝑒𝑟 × 𝑡𝑖𝑚𝑒
Power devices
Devices are appliances in the house that need electricity to
work.
The longer a device is switched on, the more electricity it will use.
Example 1:
Electricity is sold at 61c per kWh.
A geyser uses 2 500W per hour and is switched on for 12
hours. Calculate the cost of the electrical energy that
the geyser used in that time.
𝑐𝑜𝑠𝑡 𝑜𝑓 𝑒𝑛𝑒𝑟𝑔𝑦 𝑢𝑠𝑒 = 𝑘𝑤 × ℎ × 𝑐𝑜𝑠𝑡= 2500 ÷ 1000 × 12 × 61
= 1830𝑐 ÷ 100= 𝑅18.30
Saving electricity
Switch off geysers during the day.
Switch off devices at wall sockets.
Switch off lights when you leave a room.
Use fluorescent lights instead of normal light bulbs etc.
