Download Electricity

Electricity
Starter:
 What is current?
 What is it measured in?
 What is it measured by?
 Which is the series and parallel circuit? (see
board)
Current in series and parallel circuits…
• Current in a series circuit… …..is
the same, no matter where in the
circuit it is measured.
• Current in a parallel circuit…
…..add up to equal the current from
the power supply.
Question
• Which of the ammeter positions in the parallel
circuit show us the current value of the power
supply??
A1
Ans: A1 and A3
A3
A4
A2
A5
Voltage
• Voltage is a measure of how good a battery is at
pushing electrons around a circuit or how much
energy the current has. Increasing the voltage
increases the current.
• Voltage can also be called the potential
difference.
• The symbol for voltage is V. It is measured in a
unit called volts.
• Voltage is measured with a voltmeter.
• A voltmeter is connected across a component.
The positive side of the terminal must lead back
to the positive terminal of the power supply.
Voltage in series and parallel circuits
• In series the voltage is shared between
the components.
• In parallel the voltage in each branch
equals that of the power supply.
Resistance
• Resistors are components that restrict the flow
of electrons (current).
• Resistance is the voltage lost by each ampere
of current.
• The symbol for resistance is R and the unit is
Ohms, Ω.
• Resistance is calculated from the values of
current and voltage in a circuit.
• Resistance in a circuit causes electrical energy
to be transferred to heat energy.
Ohm’s Law
• Complete practical
Starter…
• In a series circuit the current is the _________
everywhere around the circuit.
• In a parallel circuit the current is ___________
between the branches of the circuit.
• In a series circuit the voltage is ____________
between the __________.
• In a parallel circuit the voltage converted by
each component ____________ the voltage
supplied by the ____________.
Resistance
Resistance is the property of a substance that
restricts the flow of electrons through it.
In series
The total resistance will always be higher than any
single resistor
Rtotal = R1 + R2 + R3
The total amount of current supplied to the circuit
decreases as more resistors are added in series
In parallel
The total resistance will always be lower than any
single resistor
The total amount of current supplied to the circuit
increases as more resistors are added in parallel
Ohm’s Law Experiment
Investigating the relationship between current,
voltage and resistance…
▫
▫
▫
▫
Follow instructions on handout
Record current and voltage readings
Draw circuit diagram into your book
Draw graph showing relationship between current,
voltage and resistance
Ohm’s Law
9.09.11
Do now:
• In a series circuit the voltage is ____________
between the __________.
• In a parallel circuit the voltage converted by
each component ____________ the voltage
supplied by the ____________.
• In a series circuit the current is the _________
everywhere around the circuit.
• In a parallel circuit the current is ___________
between the branches of the circuit.
POWER
• In an electrical circuit, power (P) refers to the
rate at which electrical energy is:
▫ Used by a component (e.g. lamp or resistor), or
▫ Supplied by a battery or power pack.
• Unit for power is the watt (W).
• 1 watt means that 1 joule (J) of electrical Energy
(E) is used per second.
Earthing
Earth wires
• Many electrical appliances have metal cases, including cookers,
washing machines and refrigerators. The earth wire creates a safe
route for the current to flow through, if the live wire touches the
casing.
• You will get an electric shock if the live wire inside an appliance,
such as a cooker, comes loose and touches the metal casing.
• However, the earth terminal is connected to the metal casing, so the
current goes through the earth wire instead of causing an electric
shock.
Equations you need to know how to
use:
• V = IR
• P = IV
•P = E
t
• RT = R1 + R2…..
Try these:
1. A multibox is plugged into the mains and is
being supplied with 240 Volts of electrical
energy.
A toaster drawing 12 Amps of current is plugged
into the multibox and switched on. How much
electrical power is the toaster using?
_______________W
2. The following information is printed on the front of a multibox:
Maximum total load:
15A
3000W
a) How much electrical power can this multi-box safely use?__________
b) How much electrical current can this multi-box safely use?__________
3. a) The multi-box is plugged into the mains and is being supplied with 240
Volts of electrical energy.
A toaster drawing 7 Amps of current is plugged into the multi-box and
switched on. How much electrical power is the toaster using?
_______________W
b) Use the answer above to explain whether or not the toaster is overloading
the multi-box
c) The toaster is used for 60 seconds before being switched off. How much
electrical energy does the toaster use during this time?
___________ (Unit) _____
• When resistors are added into a series circuit,
resistance __________(increases/decreases)?
• When resistors are added into a parallel circuit,
resistance __________(increases/decreases)?
• If I have a phone charger (R1= 3Ω), a toaster
(R2= 5Ω) and a kettle (R3= 10Ω) in a series
circuit, what would the total resistance be?