Download Electricity and Energy NAT 5

National 5 Physics
Electricity and Energy
Conservation of
Energy
Learning intentions!
❖
The principal of energy conservation and energy transfer!
You will be successful if you can:!
❖
Describe the principal of energy conservation and apply
it to examples where energy is transferred between
stores!
❖
Identify and explain ‘loss’ of energy where energy is
transferred !
❖
Calculate the efficiency of energy transfer
The Principal of Energy Conservation
❖
In physics, the law of conservation of
energy states that the total energy of an
isolated system (a system without
external influence) cannot change.
Perpetual Motion Machine
❖
A perpetual motion machine would be capable of
operating indefinitely. It would either produce more energy
than it consumed, which would violate the conservation of
energy, or it would not lose any energy, including heat loss
due to friction, which would violate the second law of
thermodynamics.!
❖
Perpetual motion machines are impossible, but attempts to
construct them, both practical and theoretical, were useful
in formulating and testing the laws of thermodynamics,
which describe how heat flows between objects.
Types of Energy
Type
Heat
Kinetic (movement)
Nuclear
Sound
Light
Chemical
Electrical
Gravitational Potential
Elastic Potential
3 example sources
Energy Stores
❖
Energy can be stored in one form or another - for
example, energy can be stored as electrical energy!
❖
Energy cannot be created or destroyed. However,
energy can be transferred between different stores. !
❖
We are continuously recycling the energy created 13.7
billion years ago at the Big Bang.
Energy Transfer
In an efficient system the useful energy out is larger than
the useful energy in Wasted
Energy Out
Total
Energy
In
Useful
Energy
Out
Energy Transfer
20w of
Light
energy
100w of
electrical
energy
80w of
Heat
energy
National 5 Example Question
When testing new demolition methods a crane lifts a T-Rex to a height
of 80m from the ground. The gain in gravitational potential energy is
6.6MJ. The crane actually uses 10.8MJ of electrical energy in raising the
T-Rex. !
!
Explain why there is a difference between these two values
Efficiency
• We
can calculate the efficiency of a system by considering
it’s input and output energy. • Efficiency
is usually expressed as a percentage.
Efficiency=
Useful energy out
Useful energy in
Efficiency
❖
Consider a light bulb. Let’s say that the bulb runs on 100J on
electrical energy and transfers 20 joules into light energy and
the rest into heat. Calculate the efficiency of the light bulb.
Power Efficiency
•A
motor is 60% efficient. What power can this motor deliver
when it receives 2000W?
Useful Power out
Efficiency=
Useful Power in
National 5 Physics
Electricity and Energy
Electrical Charge
Learning intentions!
❖
The relationship between current, voltage and resistance
in relation to electrical energy. !
You will be successful if you can:!
❖
Describe electrical charge as a property of matter. !
❖
State that static electricity is the build-up of electrical
charge on objects.
Electrical Charge
❖
A fundamental property of matter that means all
particles are either positive, negative or neutral. The
most common negatively charged particle is the
electron, and the most common positively charged
particle is the proton. Every charged particle is
surrounded by an electric field. This causes an attraction
between oppositely charged particles, and repulsion
between like charges.
Electrostatics
❖
Bring the negatively charged polythene rod towards and
then away from…!
❖
a small stream of tap water!
❖
a pile of paper pieces!
❖
the empty drinks can!
❖
another charged polythene rod balanced on a watch glass !
❖
another charged acetate rod balanced on a watch glass
Electrostatics
❖
Rub the polythene rod with the cloth. This has the effect
of transferring electrons from the cloth to the rod,
making the rod negative and the cloth positive. Putting
the rod and the cloth back together again makes the
rod/cloth system neutral again.
Charge, Current and Time
Current is the rate of charge movement and can be calculated using a
simple equation:
I=Q/t
!
I is the current measured in Amperes (A)
Q is the charge measured in Coulombs (C)
t is the time measured in seconds (s)
!
Q
I
t
Charge, Current and Time
Example!
❖
What is the current when 4C (coulombs) of charge pass
a point in 0.2 seconds?
Ultimate Physics: Using Electricity
Pg 4 -5
National 5 Physics
Electricity and Energy
Electrostatics Investigation
Electrostatics Report
❖
Draw on knowledge and understanding of the key areas of this Unit
and apply scientific skills by:!
❖
2.1 Making accurate statements!
❖
2.2 Describing an application!
❖
2.3 Describing a physics issue in terms of the effect on the
environment/society!
❖
2.4 Solving problems!
❖
Discuss and research the uses of electrostatics, for example laser
printers, paint spraying, cling film, forensic science, removal of dust,
electrostatic precipitators, electrostatic separators.
National 5 Physics
Electricity and Energy
Alternating and Direct
Current
Starter Question
1. A small generator can produce 0.6mA of
current every minute. How long will it take to
produce a charge of 3C?!
!
2. An LCD monitor draws (uses) a current of 2A.
How much charge flows to the monitor if it is
left on for 6 hours?
Learning intentions!
❖
Difference between Alternating and Direct Current !
You will be successful if you can:!
❖
Use and oscilloscope to show the wave patter of
alternating and direct current!
❖
Define electrical power as the measure of how quickly
energy is converted from one to another
A.C/D.C
Use an oscilloscope to
examine the signal of an
alternating and direct current
supply.!
You will need: !
❖
An Oscilloscope!
❖
2 cables!
❖
A.C. power supply!
❖
D.C. power supply
Sketch the signal that you
observe on the oscilloscope
when it is connected to both
an A.C. and D.C. power
supply.
Direct Current
❖
If the current flows in only one
direction it is called direct
current, or d.c. Batteries and
cells supply d.c. electricity,
with a typical battery
supplying maybe 1.5V. The
diagram shows an oscilloscope
screen displaying the signal
from a d.c. supply.
Alternating Current
❖
If the current constantly changes
direction, it is called alternating
current, or a.c.. Mains electricity
is an a.c. supply, with the UK
mains supply being about 230V.
It has a frequency of 50Hz (50
hertz), which means it changes
direction, and back again, 50
times a second. The diagram
shows an oscilloscope screen
displaying the signal from an
a.c. supply.
Why is AC used for power transmissions?
❖
When transporting electricity over large distances energy is lost. This is
due to the resistance in the wires.!
!
!
P
2
=I R
❖
This means that if the current is doubled the power loss becomes four
times greater.!
❖
However, this also means that the power loss can be greatly reduced by
reducing the current. If the current is halved the power loss will be
reduced to a quarter of its previous level.!
❖
Transformers are used to
Power
❖
Power (P) is a measure of the energy converted from
one form to another and is measured in watts (w). !
!
!
❖
Power is related to Voltage, Current and Resistance by
the following relationships
Ultimate Physics: Using Electricity
Pg 8 to13
National 5 Physics
Electricity and Energy
Power
Starter Question
Is the current from the mains supply in the
UK AC or DC? Explain why current is
distributed over long distances in this form.
Learning intention!
Power and Energy transfer!
You will be successful if you can:!
❖
Calculate your gain in potential energy as you climb a
flight of stairs!
❖
Estimate your own power as you climb a flight of stairs!
❖
Use an appropriate format to record experiment results.
Power
❖
Power (P) is a measure of the energy
converted from one from to another
and is measured in watts (w).
How much power can you develop?
❖
You could run up a flight of stairs rapidly or you could
climb the same stairs very slowly. Either way, you do
the same amount of work because you apply the same
force (equal to your weight) through the same distance
(the height of the stairs.) !
❖
Power is work per time. That is, if you do the same
amount of work in a shorter time, it takes more power.
What we will measure/record
❖
Aim: To estimate your own power as you climb a flight
of stairs
❖
Time to climb the stairs (in seconds)!
❖
Mass (in kilograms)!
❖
Height of the flight of stairs
Measuring Your Power
Aim: To estimate your own power as you climb a flight of
stairs!
You will need:!
❖
Bathroom Scales!
❖
Metre Stick/Measuring tape!
❖
Stop Clock!
❖
Flight of Stairs
Measuring Your Power
Method:!
Groups of 3!
1 timer, 1 recorder,
1 runner
❖
Measure the height of the flight of stairs!
❖
Measure your mass, in kilograms, using the bathroom
scales!
❖
❖
TAKE CARE WHEN
Record how long it takes you to climb the flight of stairs!
CLIMBING
THE
STAIRS
Calculate the potential energy gained using the equation
Ep=mgh (where m is your mass, g is the gravitational field
strength on Earth and h is the height of the flight of stairs!
❖
Calculate your power using the equation
Learning intention!
Power and Energy transfer!
You will be successful if you can:!
❖
Use an appropriate format to record experiment results.!
❖
Calculate your gain in potential energy as you climb a
flight of stairs!
❖
Estimate your own power as you climb a flight of stairs
Measuring Your Power
Mass {kg}
Gravitational Field
Stregth (m/s2)
Height of Stairs
{m}
Time (s)
Attempt 1 (s)
Attempt 2 (s)
Attempt 3 (s)
Learning intention!
Power and Energy transfer!
You will be successful if you can:!
❖
Calculate your gain in potential energy as you climb a
flight of stairs!
❖
Estimate your own power as you climb a flight of stairs!
❖
Use an appropriate format to record experiment results.
Ultimate Physics: Using Electricity
Pg 8+9 Q 2-10
National 5 Physics
Electricity and Energy
Potential Difference
Learning intention!
❖
Potential Difference (Voltage) in a circuit!
You will be successful if you can:!
❖
State that the potential difference (voltage) of a supply is
a measure of the energy given to the charge carrier in a
circuit. !
❖
State the definition of a a volt!
❖
Measure potential difference in a circuit.
What do we know already?
❖
Electricity is a flow of charge!
❖
Electricity can be used to transport energy!
❖
Electricity is potentially dangerous!
❖
Charged particles can be positive, negative or neutral
Potential Difference
❖
A battery changes chemical energy into electrical energy. !
❖
The chemical energy is carried by electrons that move round the circuit.!
❖
This electrical energy is converted into other forms of energy by
components e.g light bulbs and motors.!
❖
The amount of energy an electron has at any point around the circuit is
called their potential. !
❖
As electrons move round a circuit they transfer electrical energy into other
forms of energy. This means that the electrons have different amounts of
electrical energy (or potential) at different points around the circuit. In
other words there is a potential difference between two points in a circuit.
Potential Difference
❖
The potential difference (voltage) between the two terminals
of a battery is a measure of the electrical energy given to the
electrons by the battery. !
❖
Example: If a battery has a voltage of 1.5 Volts this means that
there is a potential difference of 1.5 Volts between the positive
and negative terminal. The battery will therefore supply each
coulomb of charge with 1.5 Joules of energy. This energy is
then carried around the circuit, and can be transformed by
components in the circuit into other forms of energy.
1 volt = 1 joule per coulomb !
1V = 1J/C
Measuring Potential Difference
To measure the potential difference across a component the
voltmeter is connected as shown:
National 5 Physics
Electricity and Energy
Potential Difference and
Current in a Circuit
Learning intention!
❖
Measuring potential difference and current in series and
parallel circuits. !
You will be successful if you can:!
❖
Measure the potential difference in both a series and
parallel circuit!
❖
Measure the current in both a series and parallel circuit!
❖
State the rules for both potential difference and current
in series and parallel circuits
Measuring Potential Difference
Task! !
❖
Build the following Circuit!
❖
Measure the potential difference across the battery and
each of the lamps and record your measurements in a table.
Component
Cell
Lamp A
Lamp B
p.d (V)
Measuring Potential Difference
Task! !
❖
❖
Can you see a
Build the following Circuit!
relationship between the
Measure the potential difference across battery voltage and the
the battery and each of the lamps and voltage across the lamps?
record your measurements in a table.
A
B
C
Component
Battery
Lamp A
Lamp B
Lamp C
p.d (V)
p.d in Series and Parallel
Series Circuit
❖
The voltage across each of the
components add up to the
supply voltage
Vs=V1+V2+V3…
Parallel Circuit
❖
The voltage in each branch is
the same as the supply voltage
Vs=V1=V2=V3…
Measuring Current
Task!
❖
Build the circuit as shown.!
❖
Measure the current in each of the positions A to D.!
❖
Record your measurements in a table.
Position
A
A
D
B
C
B
C
D
Current (A)
PARALLEL CIRCUIT
!
Task
!
!
Build the following circuit
What do you notice about the brightness of the bulbs?
Measuring Current
Task!
❖
Build the circuit as shown.!
❖
Measure the current in each of the positions A to E.!
❖
Record your measurements in a table.
A
E
Position
B
A
B
C
C
D
D
E
Current (A)
Current in Series and Parallel
Series Circuit
❖
The current is the same at
all points in a series circuit
Is=I1=I2=I3…
Parallel Circuit
❖
The current in each of the
circuit branches adds up to
the supply current
Is=Ibranch1+Ibranch2+Ibranch3…
National 5 Physics
Electricity and Energy
Resistance in series and
Parallel Circuits
Learning intention!
❖
Measuring resistance in series and parallel circuits. !
You will be successful if you can:!
❖
Measure the resistance in both a series and parallel
circuit!
❖
State the rules for resistance in series and parallel
circuits!
❖
Complete calculations involving the rules for resistance
in series and parallel circuits
What is Resistance?
What is Resistance?
All materials oppose current which flows through them. In other words
they limit the flow of charge. This opposition to the current is called
resistance. Resistance is measured in Ohms ("). !
For most materials the resistance depends upon:!
❖
The type of material - the better the conductor the lower the
resistance!
❖
The length of the material - the longer the material the higher the
resistance!
❖
The thickness of material - the thinner the material the higher the
resistance !
❖
The temperature of the material - the higher the temperature the
higher the resistance
What is a Resistor?
A resistor is a component designed to reduce the current. !
❖
A variable resistor has a resistance that can be changed. !
❖
A fixed resistor has a resistance that remains the same.
Many domestic appliances use
resistance to transfer electrical
energy to heat and light energy. !
The heating element in this kettle
is a coil of metal that resists
electricity. As current is passed
through the metal, resistance
causes the metal to get hot and so
boils the water.
Resistors in Series
❖
❖
When two (or more) resistors
are connected in series, the
combined resistance is higher
than the individual resistors. !
There is only one path for the
current to travel, which means
that it flows through the
resistors one after the other.
RT=R1+R2…
4Ω
2Ω
Resistors in Parallel
❖
❖
When two (or more) resistors are
connected in parallel, the current
splits at the branches and does not go
through each resistor. !
This means the total combined
resistance is less than any of the
individual resistors.
4Ω
2Ω
Ultimate Physics: Using Electricity
Pg 22 Q 2 and 3
Pg 23-25 Q 1 to 5
Pg 25-26 Q 1 to 5
National 5 Physics
Electricity and Energy
Ohm’s Law
Learning intention!
❖
Ohm’s Law !
You will be successful if you can:!
❖
Describe the relationship between Voltage, Current and
Resistance !
❖
Perform calculations using Ohm’s Law
Ohm’s Law Investigation
Investigate how the current and voltage change with resistance in a series
circuit.!
Components:!
❖
DC Power Supply!
❖
Variable Resistor!
❖
Resistor!
❖
Voltmeter!
❖
Ammeter!
❖
Connecting Wires
National 5 Physics
Electricity and Energy
Research Assignment
Unit 2 report
❖
Research and discuss the uses of electrostatics, for example: laser
printers, paint spraying, cling film, forensic science, removal of
dust, electrostatic precipitators, electrostatic separators.!
❖
Your essay should be around 50 to 100 words and include:!
❖
A clearly identified topic!
❖
A description of the application!
❖
The impact on society or the environment!
❖
Information presented in your own words
National 5 Physics
Electricity and Energy
Potential Dividers
Starter Question
❖
Calculate the total resistance of this circuit
200"
220"
680"
500"
Learning intention!
❖
Investigate and discuss voltage and resistance in
electrical circuits. !
You will be successful if you can:!
❖
Describe what happens to the voltage across a resistor
in a voltage divider circuit when the resistance changes.
The Voltage Divider
Aim: Investigate the effect
on voltage in a voltage
divider circuit (series
circuit) when the resistance
of R1 and R2 changes.
Results Table
Resistor 1!
(")
Resistor 2!
(")
Voltage 1!
(V)
Voltage 2!
(V)
Total Voltage!
(V)
Voltage Divider Circuit
❖
Answer the following Questions:!
❖
If you know the voltages V1 and V2 how do you
calculate the total voltage?!
❖
What happens to the voltage across the resistors (V1
and V2) when you increase the resistance of resistor R1?!
❖
If R1 is smaller than R2 then what happens to the
voltage across R1 and R2?
Calculating the Voltage
❖
To calculate the voltage across resistor R1 in the circuit,
the following equation can be used:
Voltage Dividers
❖
Voltage divider circuits can sometimes be drawn
slightly differently than you will be used to however the
same rules apply:
Example 1
12 V
30 !
30 !
Example 2
12 V
20 !
30 !
Ultimate Physics: Electronics Pg 12