Download Basic Electricity - Lesmahagow High School

BASIC ELECTRICITY
Nicola Tesla: Mad Electricity
LESSON 1 : CIRCUIT SYMBOLS
Draw and identify the circuit symbol for a
battery, lamp, switch, resistor, motor, and
variable resistor.
 State that lamps, heaters and motors and
buzzers convert electrical energy into other
forms.

LESSON 1 : CIRCUIT SYMBOLS

Examine examples of circuit components and produce
a poster matching pictures of components to their
symbols and energy conversions.
ELECTRICAL ENERGY CONVERTERS
What are the energy conversions associated with each of
these devices?
Loudspeaker
 Microphone
 Hair straighter
 TV
 Lift going up

Heater
 Lamp

electrical  sound
 sound  electrical
 electrical  heat
 electrical  sound + light
 electrical  kinetic +
potential
 electrical  heat
 electrical  light + heat

Now watch this short video: Electricity and circuits
LESSON 2/3: PRACTICAL CIRCUITS - QUIZ BOARD
LESSON 2/3: PRACTICAL CIRCUITS - TRAFFIC LIGHTS
LESSON 2/3 – PRACTICAL
CIRCUITS
- ELECTROPLATING
LESSON 4,5 ELECTRICAL MEASUREMENTS
IN CIRCUITS









State that an ammeter is used to measure current in Amps.
Draw and identify the circuit symbol for an ammeter.
Draw a circuit diagram showing the correct position of an
ammeter in the circuit.
State that current is a flow of charge and is measured in
amperes
State that an voltmeter is used to measure voltage in Volts
Draw and identify the circuit symbol for a Voltmeter.
Draw a circuit diagram showing the correct position of a
voltmeter in the circuit.
State that voltage is the electrical push and is measured in
Volts.
State that the voltage is the same for all components
connected in parallel.
LESSON 4 : ELECTRICAL MEASUREMENTS –
SERIES CIRCUIT – XMAS TREE LIGHTS
Xmas tree lights are wired in series – in a line one after
the other.
Connect three bulbs in series as shown in the diagram.
Use retort stands as model tree!
You will need:
•Connecting wire
•3 x Bulb holders with 2.5v lamps
•6V battery
•1 x retort stands and clamps
•Wire strippers
MEASURING CURRENTS IN THE
CIRCUIT
What is current?
Programs / Virtual Int1 Physics / Practical Electricity / Current
Watch as you are shown how
to measure the currents in
the circuit you have just built.
 Now go and measure the
currents from the battery and
through each of the lamps.
 Can you notice a pattern?
 The current is the same at all
points at all points in the
circuit

video clip: How to use a multimeter
MEASURING CURRENT
Current is the flow of tiny electric charges around a
circuit.
 An ammeter is used to measure the current through a
circuit, measured in amperes (A)
 To connect an ammeter we have to break the circuit
and put the ammeter in series with the other
components.
 The size of a current in a series circuit is the same at
all points in the circuit

?A
2A
?A
2A
?A
2A
MEASURING VOLTAGES IN THE
CIRCUIT
Watch as you are shown
how to measure the
voltages in the circuit you
have just built.
 Now go and measure the
voltages across the
battery and each of the
lamps.
 Can you notice a pattern?
 The voltages in a series
circuit add to equal the
battery voltage (or very
similar!)

MEASURING VOLTAGE IN SERIES




Voltage can be thought of as the 'push' it exerts on charges in
the circuit. A bigger voltage means a bigger 'push', resulting
in a larger current
A voltmeter is used to measure voltage, in volts (V)
Voltmeters are connected in parallel to either side of the
component.
The size of the voltage across the battery in a series circuit is
equal to the sum of the voltages across the other components.
3V
?V
6V
?V
3V
?V
LESSON 5 : ELECTRICAL MEASUREMENTS IN A
PARALLEL CIRCUIT – STREET LIGHTS
Street lights are wired in parallel and are controlled by a
time switch driven by a clock. This turns the lights on and
off at the correct time.
Connect three bulbs in parallel as shown in the diagram.
Use retort stands as model lamp posts.
You will need:
•Connecting wire
•3 x Bulb holders with 6v lamps
•6V battery
•3 x retort stands and clamps
•Wire strippers
•
What are the main advantages of wiring street lamps
in parallel?
MEASURING VOLTAGES IN THE CIRCUIT
Watch as you are shown
how to measure the
voltages in the circuit you
have just built.
 Now go and measure the
voltages across the
battery and each of the
lamps.
 Can you notice a pattern?
 The voltages in a
parallel circuit are all
the same (or very
similar!)

MEASURING VOLTAGE
 The
size of the voltage across the battery in a
parallel circuit is equal to the voltages across
the other components.
?V
6V
?V
6V
?V
6V
MEASURING CURRENTS IN THE CIRCUIT
Watch as you are shown
how to measure the
currents in the circuit you
have just built.
 Now go and measure the
currents from the battery
and through each of the
lamps.
 Can you notice a pattern?
 In a parallel circuit the
current from the
battery equals the sum
of the currents through
the lamps (or very
similar!)

MEASURING CURRENT IN A PARALLEL
CIRCUIT
 In
a parallel circuit:
 the size of the current from the battery
equals the sum of the currents through
each of the other components.
4A
?A
2A
?A
2A
?A
4A
?A
video clip: Lighting Circuit
ADVANTAGES OF WIRING STREET
LAMPS IN PARALLEL:
 When bulbs are connected in parallel each bulb gets
the full battery voltage.
 Each bulb lights with equal brightness.
 If one or more bulbs stop working or are removed the
rest continue lighting.
SERIES V PARALLEL SHOW-ME EXERCISE

You will see statements appear that may apply to
SERIES circuits or PARALLEL circuit. Which is it?
SERIES
PARALLEL
These have no
If one bulb
breaks,
the
branches
or
junctions
Can
be
turned
on
other bulbs in otherand off
put more
bulbs in they
byIfayou
single
switch
branches
stay
on.
will
be
dimmer
Switches
be put into
anywhere
in can
circuit
asthe
it iscircuit
harder
for
the current
to turn
on and
Thetosum
of
voltages
across
get through- the resistance
off
allhave
or part
ofisthe and
branches
is
higher
all These
the
components
circuit.
junctions
equal
to the voltage across
oneorbulb
breaks, all
theIfcell
battery
you put
theIfothers
go more
out. bulbs in
Thethey
size of
current
flowing
will
stay bright
in different parts of the
circuit can be different.
AMMETER AND VOLTMETER EXERCISES

Redraw each of the following diagrams and on each,
Add a meter to find the voltage across component E
 Add a meter to find the current through component F


Now complete the exercise, “Measuring current and
voltage in series and parallel circuits”
CURRENT AND VOLTAGE CLIPS
Current and voltage in a circuit.
 Current and Voltage in a series and parallel
circuit

LESSON
7/8: OHM’S LAW RESISTANCE
Conduct an experimental investigation of the
relationship between voltage and current
through a resistor.
 State that voltage/current = constant
 State that the “constant” is called the
“resistance”
 State that resistance is a measure of the
opposition to the flow of current in a circuit.
 State that resistance = voltage/current is called
Ohm’s law.
 Calculate resistance using Ohm’s law

INVESTIGATION: HOW DOES CHANGING
THE VOLTAGE AFFECT
THE CURRENT
?
In this experiment you will use battery voltage to
push current through a resistor.
 You will use an ammeter and a voltmeter to find
how changing the voltage affects the current.
 Follow the instructions on the worksheet,
“Voltage, Current and Resistance”

OHMS LAW 2
Number
of
batteries
1
2
3
4
Voltmeter
reading
(Volts)
Ammeter
Reading
(Amps)
voltage
current
OHM’S LAW - RESISTANCE



An experimental investigation of the
relationship between voltage and current
through a resistor shows that
 voltage/current = constant.
 this is called Ohm’s Law
The “constant” is called the “resistance”.
Resistance is a measure of the opposition to the
flow of current in a circuit.
CALCULATING RESISTANCE FROM
AMMETER AND VOLTMETER VALUES
Calculate resistance using:
voltage
resistance =
current
Example:
The current through a resistor is 0.1 amperes when the
voltage across it is 12 volts. Calculate the resistance.
0.1A
resistance =
voltage
current
12V
=
12
0.1
= 120W
OHMS LAW PRACTICE
1.
A resistor has a voltage across it of 12 volts and a current
through it of 2.5 amperes.
Calculate the resistance of the resistor.
Solution
2.
A voltage of 6 volts is across a resistor where the current
is 0.5 amperes.
What is the value of the resistor?
Solution
3.
Calculate the resistance of a component when a voltage of
24 V causes a current of 0.1 amperes.
Solution
5.
A torch bulb is marked "6 V, 0.25 A".
Calculate the resistance of the bulb.
Practical Problems involving resistance
Solution
1.
A resistor has a voltage across it of 12 volts and a
current through it of 2.5 amperes.
Calculate the resistance of the resistor.
resistance =
voltage
current
12
=
2.5
= 4.8 W
Beath High School - Int 1 Physics
29
2. A voltage of 6 volts is across a resistor where the
current is 0.5 amperes.
What is the value of the resistor?
resistance =
voltage
current
6
=
0.5
= 12 W
3. Calculate the resistance of a component when a
voltage of 24 V causes a current of 0.1 amperes.
resistance =
voltage
current
24
=
0.1
= 240 W
4. A torch bulb is marked "6 V, 0.25 A".
Calculate the resistance of the bulb.
resistance =
voltage
current
6
=
0.25
= 24 W
LESSON
9: PRACTICAL PROBLEMS
INVOLVING RESISTORS
Draw and identify the circuit symbol for a
resistor and a variable resistor.
 State that resistors convert electrical energy into
heat energy.
 State that an ohmmeter is used to measure
resistance.
 State that resistance is measured in ohms.
 State that an increase in resistance of a circuit
leads to a decrease in the current in the circuit.
 Give two practical uses of resistors.

PRACTICAL USES OF RESISTORS 1
The most common use for a resistor is simply to
control the size of the current flowing in part of a
circuit.
 The larger the resistance the smaller the current.
 The smaller the resistance the larger the current.


Resistance is measured in units of ohms (Ω)

Symbol for resistor:

Symbol for variable resistor:
PRACTICAL USES OF RESISTORS 2
Dimmer Switch
 Fan Speed
 Scaletrix controller
 Petrol Gauge
 Heating Element
 Radio volume control
 Skin Resistance – Lie Detector
