This page contains the detailed and easy notes for GCSE OCR 21st Century Physics Electric Circuits for revision and understanding Electricity.

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GCSE OCR 21st Century Physics Electric CircuitsComplete Revision Summary

Electric Circuits

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Electric Circuits

• Circuit Symbols
• Circuit Diagram
• Charge, Current, Resistance and
• Potential Difference
• Voltage-Current Graph of
• Resistor, Filament Bulb and diode
• Series Circuit
• Parallel Circuit
• Main electricity
• Power
• Energy Efficiency
• National Grid
• Static Electricity
• Magnetism
• Magnetic Poles
• Magnetic Fields
• Electromagnetism
• The motor effect
• Flemming Left Hand Rule
• Electric Motor
• Electric Loudspeakers
• Induced Potential
• Generator Effect
• Microphones
• Transformers

CIRCUIT DIAGRAM

• Draw a circuit diagram with a battery, bulb and a switch.
• How will you measure the current and potential Difference of the Circuit ?

CURRENT, POTENTIAL DIFFERENCE AND RESISTANCE

• Current is the rate of flow of charge measured in Ampere.
• One Ampere is the current flowing when one coulomb of charge flows through one second.

• Resistance is the obstruction to the flow of current measured in ohms

• Potential difference measured in Volts is the work done per unit charge.
• 1V = 1JC^-1
• One volts is the potential difference when 1 J of energy is transferred per coulomb of charge.

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CIRCUIT SYMBOLS

EXAMPLES

Q1 Calculate the current flowing when 4 C of charge flows for 2 minutes ?

I = Q/T = 4/2 X 60 S = 0.033A

Q2 Calculate the energy transferred when 2 V of potential difference creates a charge of 2 C

E = V x Q = 2 x 2 =4J

Q3 Calculate the resistance of the circuit when 4V of potential difference produces a current of 2 A.

R = V/I =4/2 = 2 Ω

Q4 Calculate the charge when 5A of current flows for 5 minutes

Q = I x T = 5 x 5 x 60 =1500C

Q5 Calculate the potential difference when 10 J of work done is done to move the charge of 5 C.

V = E/Q =10/5 = 2V

VOLTAGE-CURRENT GRAPH

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Conductor

As the voltage increases, the current Increases. The resistance is constant.

Filament Lamp

As the voltage increases, the current increases at the start but after that bulb gets heated and increase in temperature increases resistance so the current do not increases and the graph curves.

Diode

Diode conduct electricity in one direction. In reverse direction, the resistance is too high so no current flows. When it reaches a threshold voltage, the current starts to increases then linearlt.

SERIES AND PARALLEL CIRCUITS

Series Circuit

• Total Resistance is greater than individual: R 1+ R2 = R(Total)
• Current Across each component is the same: V(total)/R(Total)= I
• Voltages get divided between each component

Parallel Circuit

• Total resistance is less than individual = R(total) = R₁R₂/R₁ +R₂
• Voltage is same across is each component = V
• Current gets divided between the components
• I₁ = V/R₁ I₂ = V/R₂

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Electric Circuits

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EXAMPLE OF SERIES AND PARALLEL CIRCUITS

• Total Resistance RI + R2 = 15 Ω
• Voltage: 20V
• Current = 20/15 =1.33A
• Voltage across 5 ohms = 1.33 x 5 = 6.7V
• Voltage across 10 ohms = 1.33 X 10 = 13.3V

• Total Resistance R₁R₂/ R₁ + R₂ = 50/15 = 3.33
• Voltage: 20V
• Current = 20/3.33 =6A
• Current across 5 ohms = 20/5 = 4A
• Current across 10 ohms = 20/10 = 2A

MAIN ELECTRCITIY

Outer casing is made up of plastic as It is an insulator and Pins are made up of brass as it is a conductor and resistant to corrosion

UK MAIN SUPPLY

Voltage = 230V

Frequency = 50H₃

ELECTRIC POWER

Electrical Power = V x I

(Voltage ) x (Current)

P = I² x R [V= I x R]

P = V²/R

Q1 Calculate the current product by 200 W bulb if it generate a voltage of 10 v.

P = I x V

200/10 = I = 20

Q2 which is the fuse for this appliance. 12, 20, 23A or 25A

P = V x I

I = P/V = 200/10 = 20A

So the fuse of slightly greater than 20 A will be useful. So it has to be 23 A.

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DIRECT AND ALTERNATING CURRENT

NATIONAL GRID

• A network of cable and transformers that transmits electricity from a power station to homes and buildings.
• Step up transformer is used to increase the voltage for transmission. As higher voltage will have less current and so less loss of energy due to heating effect of current.

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STATIC ELECTRICITY

• Electricity due to the charge produced by rubbing.
• Atom is neutral. Due to rubbing there is a movement of electrons from one surface to another.
• The surface that loose electrons become positively charged and the surface that gains electron become negatively charged.

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LIKE CHARGES REPEL and UNLIKE CHARGES ATTRACT EACH OTHER

ELECTRIC FIELDS

Electric Field of line always travel from positive to negative.

It is the area around a charge object where force of electricity can be felt.

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TEST YOUTSELF

Q1 Sketch and explain the Voltage and Current graph of

1. a) Resistor
2. b) Filament Lamp
3. c) Diode

Q2 What are the components of a three pin plug

Q3 What is the voltage and frequency of UK Mains Supply ?

UK MAIN SUPPLY

Voltage = 230V

Frequency = 50H₃

Q4 How do your calculate efficiency of an appliance

Efficiency = Output Power/ Input Power x 100

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MAGNETS

Magnet has two poles. North Pole and South Pole

MAGNETIC FIELD

• Magnetic field in a bar magnet
• Field lines are from north pole to south pole.

• Magnetic field in a solenoid. Solenoid is a coil of wire.
• Field are in straight line inside the solenoid and forms the loop at the end.

• Magnetic field in a current carrying wire
• Field lines are according to the right hand rule. Thumb points in the direction of current, the fingers give the magnetic field of line.
  • If the current is upwards, the magnetic field lines is anticlockwise.
• If the current is downwards, the magnetic field lines is clockwise.

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ELECTROMAGNETS

It is the solenoid wound around an iron core. When the current is passed through a solenoid, the iron core becomes magnetised.

CIRCUIT BREAKER

It is an electromagnet which magnetised with a large flow of current and attracts the switch towards itself turning off the current.

SCRAPYARD CRANE

It has an electromagnet which is magnetised and then attracts the scap.

• When the switch is closed; the current flows through the electromagnet.
• The iron core will become magnetics and will attract the ammateur which rings the bell.

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RELAY

• A small amount of current will move the current in the electromagnet making the core magnetised.
• The core will attract the iron ammateur and will close the switch gap.
• The switch will be closed and the current will start flowing in the motor.
• A small current switch on the device with a greater current.

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MOTOR EFFECT

When a current carrying wire is placed in a magnetic field, it experiences a force.

Force can be increased by :

1. a) Increasing the current
2. b) Taking stronger magnet
3. c) Placing the coil perpendicular to the magnetic field.

FLEMMING LEFT HAND RULE

F – Force on the conductor

B – Magnetic Flux density

I – Current flowing through the conductor

L – Length of the conductor

First Finger:- Magnetic Field

Center Finger: Current

Thumb: Direction of Force

When a current passes through a coil placed in a magnetic field, the coil experiences a force and starts to rotate. The direction of force is given by left hand rule.

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ELECTRIC MOTOR

GENERATOR EFFECT

• When the magnet is moved inside and outside of the wire it produces a current in the wire due to electromagnetic induction.
• If the magnet is moved in the opposite direction the deflection is in the opposite direction
• Moving the wire or moving the coil has the same effect as both cuts the magnetic field lines.
• When the wire is connected to a built it will light up = GENERATOR EFFECT

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ALTERNATING CURRENT GENERATOR

• A coil is rotated in a magnetic field.
• Rotating coil cuts the magnetic field of lines and produces an electric current through electromagnetic induction.

DYANAMO

• Motor has slip ring commutator instead of slip rings
• So due to this commutator the current is not reversed so it gives only DC current.
• 
  

                       Split ring commutator

                                        Coil of wire connected to alternating current

Current is switched on it generated a magnet field which interact with the permanent magnetic field and produces force. When the current reverses the direction of force reverses generating sound waves.

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TRANSFORMERS

It is the device which is used to increase (step up) or decrease the voltage (step down) or the potential difference.

• Primary coil and the secondary coil is wound around the soft iron core.
• Primary coil is connected to an AC supply.

Input Voltage

• Changing Electric current in the primary coil creates a magnetic field.
• The changing magnetic field cuts along the secondary coil and produces a voltage.

Output Voltage

TRANSFORMER CALCULATIONS

 =  VP/VS=NP/NS

Vp = Voltage across primary coil

Vs = Voltage across secondary coil

Np = Number of turns in primary

Ns = Number of turns in secondary

If the number of turn in primary is 20 and input voltage is 230 V, What are the number of turns in secondary if the voltage generated in secondary is 460 V?

Vp = 230V             Np = 60

Vs = 460V              Ns = ?

 =

Ns = Np x Vs/ Vp

= 20 x 460/ 230

= 40 turns

A transformer input voltage is 230 V and the current is 20 A. What is the output voltage if the output current is 10A.

Vp = 230V             Vs = ?

Ip = 20A                 Is = 10A

Vp x Ip = Vs x Is

230 x 20 = Vs x 10

230 x 20/10 = 460V

NATIONAL GRID

Increasing voltage for transmission increases the voltage and decreases the current High current causes heating and results in loss of energy. By increasing the voltage, current is lowered and energy loss is prevented so transmission is efficient.

H x I²

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KEY TERMS

Magnet – A magnet is a material or an object that produces a magnetic field. Magnet has two poles – North Pole and South Pole

Magnetic Field Lines – The magnetic field lines are a visual tool used to represent magnetic fields. Field lines are from north pole to south pole.

Induce Magnetism – When a piece of non-magnetized magnetic material touches or approaches the pole of a permanent magnet, it becomes a magnet in itself.

North Pole – One end of the compass needle points in the North direction and is called the North Pole of the magnet

South Pole – One end of the compass needle points in the South direction and is called the South Pole of the magnet.

Solenoid – Solenoid is a coil of wire.

Electromagnets – It is the solenoid wound around an iron core.

Relay – A relay is an electric or electromechanical switch consisting of an electromagnet, an ammateur, a spring and a set of electrical contacts.

Circuit Breaker – It is an electromagnet which magnetised with a large flow of current and attracts the switch towards itself turning off the current.

Motor Effect – Motion as a result of current in a magnetic field is called the motor effect.

Flemming Left Hand Rule – When a current passes through a coil placed in a magnetic field, the coil experiences a force and starts to rotate. The direction of force is given by left hand rule.

Magnetic Flux density – Magnetic flux density (B) is defined as the force acting per unit of current per unit of length in a cable placed at right angles to the magnetic field.

Split Ring Commutator – These are rings that allow the direct current to move in the opposite direction to maintain full rotation.

Electromagnetic Induction – It is the production of voltage or electromotive force due to a change in the magnetic field.

Generator Effect – Current is produced because of the motion of a conductor in the magnetic field. Mechanical energy is transformed to electrical energy.

Transformer – It is the device which is used to increase (step up) or decrease the voltage (step down) or the potential difference.

Step Up Transformer – It is the device which is used to increase (step up) or the potential difference.

Step Down Transformer – It is the device which is used to decrease the voltage (step down) or the potential difference.

Transformer Efficiency – Efficiency of a transformer can be defined as the output power divided by the input power.

National Grid – Electricity is transferred from the power plant to consumers via the National Grid

Disclaimer:

I have tried my level best to cover the maximum of your specification. But this is not the alternative to the textbook. You should cover the specification or the textbook thoroughly. This is the quick revision to help you cover the gist of everything. In case you spot any errors then do let us know and we will rectify it.

References:

BBC Bitesize

Wikipedia

Wikimedia Commons

Image Source:

Wikipedia

Wikimedia

Commons

Flickr

Pixabay

Make sure you have watched the above videos and are familiar with the key definations before trying these questions. It is also good to time yourself while doing these questions so that you can work on the speed as well.

Electric Circuits

• Static Electricity 1 MS
• Static Electricity 1 QP
• Static Electricity 2 MS
• Static Electricity 2 QP
• Current, Potentiagy Tl Difference & Resistance 1 MS
• Current, Potential Difference & Resistance 1 QP
• Current, Potential Difference & Resistance 2 MS
• Current, Potential Difference & Resistance 2 QP
• Current, Potential Difference & Resistance 3 MS
• Current, Potential Difference & Resistance 3 QP

 Electricity In Home

• Domestic Uses & Safety 1 MS
• Domestic Uses & Safety 1 QP
• Domestic Uses & Safety 2 MS
• Domestic Uses & Safety 2 QP
• Domestic Uses & Safety 3 MS
• Domestic Uses & Safety 3 QP

Electro Magnetic Waves

• Electromagnetic Waves 1 MS
• Electromagnetic Waves 1 QP
• Electromagnetic Waves 2 MS
• Electromagnetic Waves 2 QP
• Electromagnetic Waves 3 MS
• Electromagnetic Waves 3 QP

Electromagnetism

• Induced Potential, Transformers & National Grid 1 MS
• Induced Potential, Transformers & National Grid 1 QP
• Induced Potential, Transformers & National Grid 2 MS
• Induced Potential, Transformers & National Grid 2 QP
• Induced Potential, Transformers & National Grid 3 MS
• Induced Potential, Transformers & National Grid 3 QP
• Motor Effect 1 MS
• Motor Effect 1 QP
• Motor Effect 2 MS
• Motor Effect 2 QP
• Permanent & Induced Magnetism 1 MS
• Permanent & Induced Magnetism 1 QP
• Permanent & Induced Magnetism 2 MS
• Permanent & Induced Magnetism 2 QP