Electricity & Energy Nat.

Electricity & Energy Nat

By the end of this lesson I will be able to…
define electric charge in terms of positive and negative recognise that an electric field exerts a force on a charged particle within the field

Charge Experiment Watch glasses Charged rod Effect Charged Rod
Attracts Repels Polythene (-ve) Acetate (+ve)

Types of electrical charge
It was realised that there are 2 types of “electrical charge” These are called positive & negative We will be dealing with electrons - negative charge carriers

Static Electricity When aeroplanes refuel there is a risk of fire from a static spark Static Discharge Reels are connected to the plane to drain away any build up of electrical charges

Uses of Static Electricity
Spray painting cars Photocopier Removal of pollutant particles from the air Dangers of Static Electricity

The Effect of an Electric Field on a Negative Charges

The Effect of an Electric Field on Charges
An electric field is an area in which a charged particle will experience a force. The following diagram shows an electric field between two charged plates. The normally invisible lines have been drawn to show the direction of the electric field. If a negative charge is placed within this electric field it will be attracted to the positive plate. A positive charge will be attracted to the negative plate . An electric field can also exist around a single point charge

understand electrical current as the electrical charge transferred per unit time. use appropriate relationship to carry out calculations involving charge, current and time.

Moving Charges! If the electrical charges are moving we have current electricity Current electricity is used to make all our everyday electrical appliances work….

Charge & Current Charges (electrons) move in a circuit.
Charge is measured in Coulombs (C) The letter ‘Q’ is used to represent Charge!

Charge & Current Current is a flow of charge (electrons) in a circuit.
Current is measured in Amperes or Amps (A). The letter ‘I’ is used to represent Current! 1 Amp is equal to 1 Coulomb of charge per second.

Charge & Current Charge & current are linked by the relationship:
Q = I x t s seconds t Time C Coulomb Q Charge A Amp I Current Unit symbol Unit Symbol Quantity

Example In a lightning storm 20,000 coulombs of charge are transferred in half a second. What is the electrical current? Q = C t = 0.5 s I = ? Q = I x t 20000 = I x 0.5 I = / 0.5 I = 40,000 Amps

recognise that an electric field exerts a force on a charged particle within the field

recognise that the potential difference (voltage) is a measure of the electrical energy the supply gives to each coulomb of charge which flows through it describe the difference between alternating and direct current State the value for mains voltage

Potential Difference (Voltage)
The parallel plates will have a voltage across them this called the potential difference. This has the symbol V and is measured in volts (V). The potential difference is a measure of the energy given to the charges when they move between the plates.

Direct Current (d.c) Direct current (d.c) is current that flows in one direction around a circuit. A battery is an example of a supply of direct current

Alternating current (a.c)
Alternating current (a.c) is where the current repeatedly changes direction. The mains supply is an example of alternating current The frequency of mains current is 50 Hz. This means that it changes direction 50 times per second. Mains voltage is set at 230 V

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 what happens to the current in a series circuit State what happens to the voltage in a series circuit State what happens to the current in a parallel circuit State what happens to the voltage in a parallel circuit

Current & Voltage Current is a flow of electrons, which have a negative charge. The current can be measured using an ammeter. Current has the unit ampere or amps for short (A). The voltage (potential difference) is a measure of the energy given to the electrons) Voltage can be measured using a voltmeter. Voltage has the unit volts (V).

Using an Ammeter An ammeter is placed in series with the other electrical components to measure the current. Ammeter

Using a Voltmeter A voltmeter is placed in parallel across the component that you are measuring. Voltmeter

Current in a Series Circuit
The current in a series circuit is the same at all points. This is because the current only has one path to flow round.

Voltage in a Series Circuit
The voltage in a series circuit splits up across the components, however they all add up to the supply voltage. V1 = V2 = V3 = V

Current in a Parallel Circuit
1. 2. The current in a parallel splits up across the branches. The currents across each branch add up to the supply current. 3.

Voltage in a Parallel Circuit
The voltage in a parallel circuit is the same across each branch. V V1 = V2 = V3 =

IMPORTANT CIRCUIT RULES
In a series circuit: The current is the same at all points. The voltage splits up across the components In a parallel circuit: The current splits up through the branches The voltage is the same across each branch

Use my knowledge on series and parallel circuits to answer questions

Circuit Question 1

Circuit Question 2

Circuit Question 3

Identify a component in a circuit by investigating its relationship with current

Identifying the Unknown Component
+ - Low Voltage Supply A Set up the following circuit and measure the current Now add in the unknown component’s A-D where the ‘?’ is positioned R + - Low Voltage Supply A ? Record your results in a table

Unknown Component Current (A) Brightness Scale (1-5) No component A B C D

Resistance A resistor opposes the flow of current
Resistance has the symbol R and the unit ohms, Ω. An ohmmeter is used to measure the resistance directly If the resistance in a circuit increases, the current in the circuit ___________.

Using an Ohmmeter Always start off with the smallest scale
If you get a reading like below, increase the scale on the ohmmeter Resistor Resistance (Ω) 1 2 3 4 5

Investigate the relationship between resistance, current and voltage

Quick reminder Current – the flow of charges in an electrical circuit.
Voltage – Measure of the energy per coulomb of charge in an electric circuit. Resistance – Opposition to flow of charges in a circuit.

Voltage and Current Across a Resistor
This experiment is investigating the relationship between voltage and current across a resistor in a circuit. Voltage (V) Current (A) Voltage Current Draw a graph of your results: With current (I) on x-axis and Voltage (V) on y-axis

Conclusion V/I for a resistor remains approximately constant for different currents. R = V / I This relationship is normally called Ohm’s Law It is often written as V = IR

Example If the electric current in a toaster is 6.5 Amps what will the resistance of the heating element be? A 6.5 V light bulb has a resistance of 100 Ω. Calculate the value of the current flowing through the resistor. A 10 kΩ resistor has a current of 1.3 A through it. Calculate the voltage across the resistor

Describe the function and application of a variable resistor Carry out calculations involving current, resistance and voltage with a across a variable resistor

Starter Question The following circuit is set up. If the value on the ammeter is 0.05 A and the value on the voltmeter is 8 V, calculate the value of the resistance

Variable Resistor A resistance of a variable resistor can be altered.
The symbol for a variable resistor is: A variable resistor can be used in a variety of places. E.g. Dimmer switch, volume control on a radio

Example The variable resistance has a range from 10 Ω to Ω. What resistance would allow the bulb to shine the brightest? The voltmeter reads 5 V and the current reads 0.25 A. Calculate the resistance of the bulb. If the batteries have a supply voltage of 24 V, what is the voltage across the variable resistor?

Investigate the relationship between the current through a bulb and the voltage across it

The Effect Temperature has on resistance
Aim: Investigate the relationship between the current through a bulb and the voltage across it Apparatus 6V lamp Power pack 2 multimeters connecting leads. - + A V

Voltage (V) Current (A) Voltage Current Draw a graph of voltage against current (Voltage on Y-axis, Current X-axis)

The filament lamp does not follow Ohm's Law. The resistance of a filament lamp increases as the temperature of its filament increases. As a result, the current flowing through a filament lamp is not directly proportional to the voltage across it. Remember the gradient of the line tells us the resistance. As it is not a straight line then the resistance is changing

To investigate the relationship for calculating the total resistance in a series and parallel circuit Use an appropriate relationship to calculate the resistance of resistors in series

Resistors in series

Resistors in parallel Results
Connect resistors in parallel in various combinations Measure the total resistance each time. What happens to the total resistance when you add more resistors in parallel? Ω Results R1 (W) R2 (W) R3 (W) Rtotal (W) 1/R1 1/R2 1/R3 (W) 1/Rtotal (W)

What have we learned? Adding resistors in series increases the total resistance Rs = R1 + R2 Adding resistors in parallel decreases the total resistance 1/Rp = 1/R1 + 1/R2 If you have two identical resistors in parallel the total resistance is half the resistance of one resistor

Resistors in Series Examples
Four resistors are placed in series. If the values of the resistors are 14 Ω, 25 Ω, 100 Ω and 220 Ω, calculate the total resistance. 12 Ω 32 Ω 56 Ω Ω If all resistors have a value of 100 Ω, what is the total resistance?

Resistors in Parallel Examples
Two resistors are placed in series. If the values of the resistors are 25 Ω and 50 Ω calculate the total resistance. 100 Ω 50 Ω 200 Ω If two resistors, both with a value of 40 Ω, are placed in parallel. Calculate the total resistance

Identify a potential divider circuit State that the higher the resistance of a resistor, the greater the share of the volatge it takes Carry out calculations on potential dividers

Potential Dividers R1 = V1 R2 V2
When a circuit is made in the configuration shown, it is often called a potential divider, or a voltage divider. This is because each resistor takes a proportion of the total potential difference (voltage). How big a share of the potential difference each resistor takes depends on the size of the resistor The higher the resistance, the higher the potential difference across the resistor. R1 = V1 R2 V2

Potential Divider Relationship
9 Ω 10 V 1 Ω The above equation can be used to work out V1 or V2. If used to calculate V2 then the R1 on the top changes to R2

Potential Divider Examples
a) Calculate V1 b) Calculate the missing resistor

Circuit Question

State what is meant by the term power Measure the power of different appliances & work out how much energy it uses in a minute Calculate power, energy or time

Power All appliances have power ratings. This tells us how much energy is transferred in a second. E.g. 100 W Lamp = 100 J of energy is being transferred in a second We can calculate the power of an appliance or component by using the following equation: Power = Energy P = E time t Power is measured in Watts (W), Energy in Joules (J) and Time in Seconds (s)

Power Rating Plate

Example A toaster is rated at 1000 watts by the manufacturer. If it takes 45 seconds to toast bread, how much energy does it use? P = 1000W t = 45 s E = ? E = P x t E = 1000 x 45 E = 45,000 Joules ( E = 45kJ )

Set up a circuit to measure the current through a lamp and the voltage across the lamp Use the results from my experiment to establish a relationship between power, current and voltage Carry out worked example using this relationship

Power, Current & Voltage Experiment
Aim: To determine the relationship between power, current, and voltage. The power rating of an appliance can be determined by measuring the current through it and voltage across it when it is in use. - + A V Lamp Power Rating (W) Voltage across lamp (V) Current through lamp (A) Current x Voltage 24 12 36 48

Example 1 A toaster has a power rating of 1000 watts. If it is plugged into the mains (230 Volts) what size of current does it get it ? P = 1000W V = 230 V I = ? P = I x V 1000 = I x 230 I = 1000/230 I = 4.3 A

Use P = I V to calculate the power, current or the voltage

Starter A XBOX has a power rating of 280 watts. If it is plugged into the mains, what size of current is drawn? P = 280W V = 230 V I = ?

P=IV Questions A power saw draws 18.0 amps at 250 V. What is the power rating of the saw ? What current is drawn by a 600 W toaster connected to a 120 V outlet ? An electric fan uses 65 W of power, with a current of 5.0 A, calculate the voltage across the fan

Other Power Formulae Substituting the equations V = IR and I = V/R
in the equation: P = IV can give us another two power equations:

Example 1 P = 1000W I = 4.3 A R = ? P = I2R 1000 = 4.32 x R
A 1000 Watt toaster draws a current of 4.3 Amps. What is the resistance of the heating element? P = 1000W I = 4.3 A R = ? P = I2R 1000 = 4.32 x R R = 1000/4.32 R = 54 W

Example 2 P = 3000 W V = 230 V R = ? P = V2/R 3000 = 2302/R
A 3 kW kettle is plugged into the “mains” electricity supply. What is the resistance of the heating element? P = 3000 W V = 230 V R = ? P = V2/R 3000 = 2302/R R = 2302/3000 R = 17.6 W

Carry out calculations on power by selecting the correct formula

describe the function and application of standard electrical and electronic components: cell, battery, lamp, switch, resistor, variable resistor, voltmeter, ammeter, LED, motor, loudspeaker, photo voltaic cell, fuse, diode, capacitor, thermistor, LDR

(Light Dependent Resistor)
Component Name Circuit Symbol Function Cell Supplies electrical energy to a circuit, the longer line shows the positive side. Battery A battery of cells means 2 or more cells. DC Supply Supplies electrical energy to a circuit in the form of a direct current. AC Supply Supplies electrical energy to a circuit in the form of an alternating current. Lamp A lamp lights when current flows through it, converting electrical energy to light energy. Switch A switch allows you to complete or break a circuit. Resistor A resistor restricts the flow of current, this may be to protect other components. Variable Resistor A resistor, the resistance of which can be varied in the circuit, could be used for a dimmer switch. LDR (Light Dependent Resistor) Can be used to control a circuit. The resistance goes down as the light increases. Thermistor The resistance of a thermistor will increase as the temperature increases. Fuse A fuse is a safety device – the metal core will melt when too much current is flowing in the circuit.

Voltmeter Must be placed in parallel to measure the difference in electrical potential between two points. Ammeter Must be placed in series to measure the current flowing in a circuit. Ohmmeter Measures resistance. Must be placed in parallel with the component(s) which are to be measured. Capacitor Used to store electrical charge, can be used to create a simple timing circuit, or in the flash in a camera. Diode Only allows current to flow in one direction. Photovoltaic Cell Converts light energy to electrical energy, can be used as the power source in a circuit. More light will mean a greater p.d. across the cell. LED (Light Emitting Diode) Emits light when a current flows but only allows current to flow in one direction. Requires less energy than a lamp. Motor Converts electrical energy into kinetic energy by turning. Loudspeaker Converts electrical energy into sound energy.

State what LED stands for Identify a LED in a circuit Correctly position a LED in a circuit to allow it to light Explain why a LED has a resistor placed in series with it

LED LED stands for Light Emitting Diode The symbol for a LED is
A LED must be placed in a circuit the correct way, if not it will not light. This is because the LED, like all diodes, only allow current to flow through in one direction. A resistor is always placed in series to reduce the current through the LED so it protects the LED.

LED Calculation A LED takes a current of 12.5 mA when the voltage across it is 2 V. Draw a suitable circuit Calculate the value of the series resistor needed to operate the LED from a 9 V battery.

State the function of a fuse Investigate the effect a change in temperature has on the resistance of a thermistor Investigate the effect a change in light level has on the resistance of a LDR

Investigate the effect a change in temperature has on the resistance of a thermistor
Place the thermistor into hot water After 1 minute, take the temperature & the reading on the ohmmeter Repeat this for 5 minutes Time (min) Temperature (oC) Resistance (Ω) Investigate the effect a change in light has on the resistance of a LDR Cover the LDR with your finger & record the reading on the ohmmeter Remove your finger & record the reading on the ohmmeter Dark Light Resistance (Ω)

Thermistor & LDR Thermistor The symbol for a thermistor is
When the temperature increases, the resistance decreases. When temperature decreases the resistance increases. LDR (light dependant resistance) The symbol for a LDR is When the light level increases, the resistance decreases. When the light level decreases, the resistance increases.

State the function of a capacitor Identify a capacitor in a circuit diagram State what factors effect the time it takes a capacitor to charge up

Capacitor A capacitor is a device that stores charge & energy
The symbol for a capacitor is The time it takes a capacitor to charge up depends on the size of the capacitor and the size of the resistance The bigger the capacitor, the ________ it takes to fully charge up The bigger the resistance, the _________ it takes to fully charge up

State the function of a transistor Identify a transistor in a circuit diagram Explain how a transistor switches on in a switching circuit

The Transistor A transistor is an electronic switch that has no moving parts The symbols for a transistor are: Transistors switches on when the voltage across it is greater than a certain value NPN Transistor MOSFET

Switching Circuit - Thermistor
Temperature Down Temperature Up

Switching Circuit - LDR
Light Level Down Light Level Up

State the function of a capacitor Set up a circuit with a capacitor which demonstrates charging and discharging Give a practical example where a capacitor is used

Capacitor A capacitor stores charge between 2 parallel plates.
When connected to a supply as shown a capacitor will charge up. It can take time to charge up. The time taken depends on the size of the capacitor and the size of the resistor (if one). If these are large, then it takes longer to charge up The voltage across the capacitor cannot be greater than the supply voltage

State what is meant by pressure State what factors effect the pressure on an object State and use the relationship for calculating the pressure acting on an object

Pressure Pressure is defined as the amount of force acting at right angles to a surface The pressure exerted on a surface depends on the size of the force and the area it is exerted over We can calculate pressure by using the following equation: Pressure = Force P = F Area A Pressure = Pascals (Pa) Force = Newtons (N) Area = meters 2 (m2)

Example 1 A box with a weight of 230N is resting on a shelf. If the area of the box in contact with the shelf is 0.95 m2, calculate the pressure exerted on the shelf.

Example 2 A crate of mass 25 kg is sat on a flat surface. The surface area of the crate is 2 m2, calculate the pressure exerted on the surface.

Example 3 A pick up truck has a mass of 2600 kg. If each tyre has a contact area of 0.03 m2 with the road, calculate the pressure exerted on the road by the truck

Example 4 What happen to the pressure exerted on the floor when you stand on one foot instead of two? Explain your answer

Gas Pressure Gas particles in a container creates pressure by the particles striking the walls of its container. If they strike the walls more or harder then the pressure increases.

State that the pressure of a fixed mass of gas at constant temperature is inversely proportional to its volume.

Example 1 A 0.55 m3 container has a pressure of Pa. If the volume of the container is reduced to 0.22 m3, calculate the new pressure.

Example 2 A syringe filled with a gas has a volume of 15cm3. The pressure at this volume is Pa. The plunger in the syringe is moved and the new pressure is measured to be Pa. What is the new volume?

Example 3 A piston in a car engine moves up and down in a cylinder. When the piston is extended the volume of the cylinder is 200 ml and its pressure is x 105 Pa. When the piston is compressed the volume of the cylinder is reduced to 25 ml. Calculate the new pressure

carry out calculations to convert between C and K explain what is meant by absolute zero of temperature state that the pressure of a fixed mass of gas at constant volume is directly proportional to its temperature measured in Kelvin.

Example 1 A box containing a gas at a temperature of 295 K is heated. If the initial pressure was 1.5 x 105 Pa, calculate the pressure after it was heated to 365 K

Example 2 A syringe containing air initially has a temperature of 21 oC. If the temperature is reduced to 16 oC and its pressure is changed to x 105 pa, calculate the initial pressure

Example 3 The gas in a balloon is at a temperature of 18 oC and its pressure is Pa. If the balloon is placed into a hotter room its pressure changes to Pa. What is the temperature of the hotter room in oC?

state that the volume of a fixed mass of gas at constant pressure is directly proportional to its temperature measured in Kelvin

Example 1 A box containing a gas at a temperature of 293 K is heated. If the initial volume is 0.5 m3, calculate the volume after it was heated to 345 K

Example 2 A syringe containing air initially has a temperature of 5 oC. If the temperature is reduced to -7 oC and its volume changes to 2x10 -6 m3, calculate the initial volume

Carry out calculations involving temperature, pressure and volume of a fixed mass of gas using the general gas equation.

The General (combined) Gas Law
In the equation sheet this is given as PV = constant T Only use this equation when the question gives you 5 out of the 6 values. When it is gives you 3 values, use one of the 3 equations at the top

Example 1

Example 2 Inside a car engine, air & fuel are drawn into the cylinder at 1.01 x 105 Pa at a temperature of 40 oC and a volume of 200 cm3. During compression, the air & fuel mixture is compressed to 20 cm3 at a pressure of 4 x 105 Pa. Find the temperature of the fuel/ air mix after compression

describe the kinetic model of gas and use it to explain some of the know properties of gases

Kinetic Theory of Gases
The kinetic model of matter explains the behaviour of gases using a model. Volume The volume of a gas is taken as the volume of the container. The volume occupied by the particles themselves is so small it is neglected. Pressure The pressure of the gas is caused by the particles striking the walls of the container. Pressure is increased if there are more frequent collisions with the walls. Pressure is also increased when the particles strike the walls harder Temperature The temperature of a gas depends on the kinetic energy of the particles, the greater the kinetic energy, the greater the temperature

Kinetic Theory Questions
Explain what happens to the pressure exerted on a tyre on a hot day

Kinetic Theory Questions
2. Explain what happens to the pressure acting on a syringe when the volume is increased

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