Electricity

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Electricity
W Richards Worthing High School
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Basic ideas
Electric current is when electrons start to flow
around a circuit. We use an _________ to measure
it and it is measured in ____. Potential
difference (also called _______) is how big the
push on the electrons is. We use a ________ to
measure it and it is measured in
______. Resistance is anything that resists an
electric current. It is measured in _____.
(Words volts, amps, ohms, voltage, ammeter,
voltmeter)
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More basic ideas
If a battery is added the current will ________
because there is a greater _____ on the electrons
If a bulb is added the current will _______
because there is greater ________ in the circuit
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Current in a series circuit
In other words, the current in a series circuit
is THE SAME at any point
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Current in a parallel circuit
A PARALLEL circuit is one where the current has a
choice of routes
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Current in a parallel circuit
If the current here is 6 amps
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Voltage in a series circuit
2V
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Voltage in a series circuit
4V
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Voltage in a parallel circuit
4V
4V
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Summary
In a SERIES circuit Current is THE SAME at any
point Voltage SPLITS UP over each component
In a PARALLEL circuit Current SPLITS UP down
each strand Voltage is THE SAME across
eachstrand
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An example question
6V
A3
3A
A1
V1
A2
V2
V3
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Advantages of parallel circuits

• There are two main reasons why parallel circuits
  are used more commonly than series circuits
• Extra appliances (like bulbs) can be added
  without affecting the output of the others
• If one appliance breaks it wont affect the
  others either

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Resistance
The resistance of a component can be calculated
using Ohms Law
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An example question

• What is the resistance across this bulb?
• Assuming all the bulbs are the same what is the
  total resistance in this circuit?

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Current-voltage graphs
2. Bulb
3. Diode
1. Resistor
Explain the shape of each graph
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Three simple components

• Diode only lets current flow in one direction
• Light dependant resistor resistance DECREASES
  when light intensity INCREASES
• Thermistor resistance DECREASES when
  temperature INCREASES

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Wiring a plug
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DC and AC
V
DC stands for Direct Current the current only
flows in one direction
Time
1/50th s
AC stands for Alternating Current the current
changes direction 50 times every second
(frequency 50Hz)
240V
T
V
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Fuses
Fuses are _______ devices. If there is a fault
in an appliance which causes the ____ and neutral
(or earth) wire to cross then a ______ current
will flow through the _____ and cause it to
_____. This will break the _______ and protect
the appliance and user from further _____.
Words large, harm, safety, melt, live, circuit,
fuse
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Circuit breakers
If the current becomes too high the __________ is
activated. This will ______ the iron and the
contact will be _______. This will break the
circuit. Circuit breakers have two main
advantages over fuses they work ______ and can
easily be ______.
Words electromagnet, broken, attract, reset,
quicker
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Earth wires
Earth wires are always used if an appliance has a
_____ case. If there is a _____ in the
appliance, causing the live wire to ______ the
case, the current _______ down the earth wire
and the ______ blows.
Words fuse, fault, metal, surges, touch
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Power and fuses
Power is the rate of doing work. The amount of
power being used in an electrical circuit is
given by
Power voltage x current in W in V
in A
Using this equation we can work out the fuse
rating for any appliance. For example, a 3kW
(3000W) fire plugged into a 240V supply would
need a current of _______ A, so a _______ amp
fuse would be used (fuse values are usually 3, 5
or 13A).
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Power and fuses
Copy and complete the following table
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Charge (Q)
As we said, electricity is when electrons move
around a circuit and carry energy with them.
Each electron has a negative CHARGE. Charge is
measured in Coulombs (C). We can work out how
much charge flows in a circuit using the equation
Charge current x time (in C) (in A)
(in s)
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Example questions

• A circuit is switched on for 30s with a current
  of 3A. How much charge flowed?
• During electrolysis 6A was passed through some
  copper chloride and a charge of 1200C flowed.
  How long was the experiment on for?
• A bed lamp is switched on for 10 minutes. It
  works on a current of 0.5A. How much charge
  flowed?

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Energy and charge
The amount of energy that flows in a circuit will
depend on the amount of charge carried by the
electrons and the voltage pushing the charge
around
Energy transferred charge x voltage (in
J) (in C) (in V)
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Example questions

• In a radio circuit a voltage of 6V is applied and
  a charge of 100C flows. How much energy has been
  transferred?
• In this circuit the radio drew a current of 0.5A.
  How long was it on for?
• A motor operates at 6V and draws a current of 3A.
  The motor is used for 5 minutes. Calculate a)
  The motors resistance, b) the charge flowing
  through it, c) the energy supplied to it
• A lamp is attached to a 12V circuit and a charge
  of 1200C flows through it. If the lamp is on for
  10 minutes calculate a) the current, b) the
  resistance, c) the energy supplied to the bulb.

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Comparing magnets and solenoids
Magnet
Solenoid
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Electromagnets

• The strength of an electromagnet can be increased
  by doing three things
• Increasing the voltage
• Increasing the number of coils
• Inserting an iron core

(The poles can be reversed by reversing the
direction of the current)
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Electromagnetic induction

• The direction of the induced current is reversed
  if
• The magnet is moved in the opposite direction
• The other pole is inserted first

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Electromagnetic induction

• The size of the induced current can be increased
  by
• Increasing the speed of movement
• Increasing the magnet strength
• Increasing the number of turns on the coil

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AC Generator

• Induced current can be increased in 4 ways
• Increasing the speed of movement
• Increasing the magnetic field strength
• Increasing the number of turns on the coil
• Increasing the are of the coil

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The National Grid
Electricity reaches our homes from power stations
through the National Grid
If electricity companies transmitted electricity
at 240 volts through overhead power lines there
would be too much ______ loss by the time
electricity reaches our homes. This is because
the current is ___. To overcome this they use
devices called transformers to step up the
voltage onto the power lines. They then ____
____ the voltage at the end of the power lines
before it reaches our homes. This way the
voltage is _____ and the current and power loss
are both ____.
Words step down, high, power, low, high
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Transformers
Transformers are used to _____ __ or step down
_______. They only work on AC because an
________ current in the primary coil causes a
constantly alternating _______ ______. This will
_____ an alternating current in the secondary
coil.
Words alternating, magnetic field, induce, step
up, voltage
We can work out how much a transformer will step
up or step down a voltage
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Static electricity
Static electricity is when charge build up on
an object and doesnt move, e.g. rubbing a rod
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Two different rods will attract each other if
they have different charge
Two rods made of the same material will repel
each other due to having the same charge
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Van de Graff generators
A charge builds up on the dome due to electrons
being ______ off by the belt. If a big enough
______ is built up then the voltage becomes high
enough to _____ the air molecules and the
electrons ___ down to Earth this is an
electric _________.
Words charge, jump, current, rubbed, ionise
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Use of static 1 - Photocopiers
Photocopiers use static electricity. They work
by 1) Copying an ______ of the page onto a
______ plate, 2) Light then causes the charge to
____ away, leaving an electrostatic impression
of the page, 3) The charges left on the plate
______ small drops of black powder, 4) The powder
is transferred from the plate onto the _____, 5)
The paper is _____ to fix the powder.
P
Words heated, leak, paper, image, charged,
attract
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Use of static 2 - Printers
Inkjet printers work by spraying charged drops of
ink onto a page. The droplets can be directed
using two oppositely charged plates. The voltage
on these plates can be easily swapped or varied.
The inkjet cartridge can also moved across the
page by the printer
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Dangers of static
During refuelling the fuel gains electrons from
the pipe, making the pipe positive and the fuel
negative. The resulting voltage may cause a
spark bad news!
Solution Either earth the fuel tank with a
copper rod or connect the tanker to the plane by
a copper conductor.
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Electrolysis
Electrolysis is used to extract a HIGHLY REACTIVE
metal.
When we electrolysed copper chloride the negative
chloride ions moved to the positive electrode and
the positive copper ions moved to the negative
electrode OPPOSITES ATTRACT!!!
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Some example questions

• A current of 2A flows through some copper
  chloride for 1 minute and 0.01g of copper is
  deposited at the negative electrode.
• a) How much would be deposited if the current
  was increased to 6A?
• b) How much would be deposited if the current
  was kept at 6A and the experiment was left for
  another minute?
• c) How much charge flowed in question (b) above?
• 2) A current of 0.05A flows through some copper
  chloride for 500 seconds and 0.05g of chlorine is
  released at the positive electrode.
• a) How much would be deposited if the current
  was increased to 0.1A?
• b) How much would be deposited if the current
  was kept at 0.1A and the experiment was left for
  250 seconds instead?
• c) How much charge flowed in question (b) above?