Section 2: Electricity
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a) Units
2.1: Use the following units: ampere (A), coulomb (C), joule (J), ohm (Ω), second (s), volt (V), watt (W)
Ampere: Used to measure electrical current
Coulomb: Used to measure electrical charge
Joule: Used to measure amount of energy
Ohm: Used to measure electrical resistance
Second: Used to measure time
Volt: Used to measure energy transferred
Watt: Used to measure power
Ampere: Used to measure electrical current
Coulomb: Used to measure electrical charge
Joule: Used to measure amount of energy
Ohm: Used to measure electrical resistance
Second: Used to measure time
Volt: Used to measure energy transferred
Watt: Used to measure power
b) Mains electricity
2.2: Understand and identify the hazards of electricity
Frayed cables
Frayed cables are an electrical hazards because they expose the metal wire underneath which could lead to electrocution
Long cables
Long cables expose a tripping hazard which could lead to injury
Damaged plugs
Damaged plugs also expose the metal wire which could lead to electrocution
Water around sockets
Water is a conductor of electricity; the electricity from the socket could easily be conducted by the water which could lead to electrocution
Pushing metal objects into sockets
Metal objects are conductors of electricity; by pushing a metal object into a socket, electricity could flow into your body by flowing through the metal object first; this could lead to electrocution
Frayed cables
Frayed cables are an electrical hazards because they expose the metal wire underneath which could lead to electrocution
Long cables
Long cables expose a tripping hazard which could lead to injury
Damaged plugs
Damaged plugs also expose the metal wire which could lead to electrocution
Water around sockets
Water is a conductor of electricity; the electricity from the socket could easily be conducted by the water which could lead to electrocution
Pushing metal objects into sockets
Metal objects are conductors of electricity; by pushing a metal object into a socket, electricity could flow into your body by flowing through the metal object first; this could lead to electrocution
2.3: Understand the uses of insulation, double insulation, earthing, fuses and circuit breakers in a range of domestic appliances
Insulation
Insulation is when a non-conductor of electricity such as plastic or rubber is used as the casing for an appliance rather than a conductor. A non-conductor is called an insulator.
Double insulation
Double insulation is when none of the electric parts of an appliance can be touched by the user; as well as the wiring being insulated, the outer casing of the appliance is also made of an insulating material such as plastic.
Earthing
When an airplane is flying, it picks up electrical charges. When it lands, the plane is immediately earthed so that the electrical charges can escape the plane into the ground. If the plane was not earthed, there is a risk of the electrical charges igniting the fuel.
Fuses
A fuse is a safety device with a thin wire inside it. The wire has a low melting point. The fuse will blow if the wire gets too hot. This will shut down the circuit.
Circuit breakers
If the circuit overheats, the circuit breaker opens, breaking the circuit.
Insulation
Insulation is when a non-conductor of electricity such as plastic or rubber is used as the casing for an appliance rather than a conductor. A non-conductor is called an insulator.
Double insulation
Double insulation is when none of the electric parts of an appliance can be touched by the user; as well as the wiring being insulated, the outer casing of the appliance is also made of an insulating material such as plastic.
Earthing
When an airplane is flying, it picks up electrical charges. When it lands, the plane is immediately earthed so that the electrical charges can escape the plane into the ground. If the plane was not earthed, there is a risk of the electrical charges igniting the fuel.
Fuses
A fuse is a safety device with a thin wire inside it. The wire has a low melting point. The fuse will blow if the wire gets too hot. This will shut down the circuit.
Circuit breakers
If the circuit overheats, the circuit breaker opens, breaking the circuit.
2.4: Understand that a current in a resistor results in the electrical transfer of energy and an increase in temperature, and how this can be used in a variety of domestic contexts
The function of an electrical resistor is to slow down the movement of electrons (the current). As the movement of electrons is slowed, the kinetic energy that was moving them is converted to heat energy. This can be applied using hair dryers or heaters.
The function of an electrical resistor is to slow down the movement of electrons (the current). As the movement of electrons is slowed, the kinetic energy that was moving them is converted to heat energy. This can be applied using hair dryers or heaters.
2.5: Know and use the relationship between power, current and voltage, and apply the relationship to the selection of appropriate fuses
Power = current x voltage
P = I x V
Power = current x voltage
P = I x V
2.6: Use the relationship between energy transferred, current, voltage and time
Energy transferred = current x voltage x time
E = V x I x t
Energy transferred = current x voltage x time
E = V x I x t
2.7: Understand the difference between mains electricity being alternating current (a.c.) and direct current (d.c.) being supplied by a cell or battery
An alternating current causes the current to change continuously, with electricity flowing in one direction then the other. Direct current is when a battery makes electricity flow in one direction only.
An alternating current causes the current to change continuously, with electricity flowing in one direction then the other. Direct current is when a battery makes electricity flow in one direction only.
c) Energy and potential difference in circuits
2.8: Explain why a series or parallel circuit is more appropriate for particular applications, including domestic lighting
In a series circuit, the same current flows through all the components as there are no alternative routes at any point. Any break in the circuit will stop the current flowing and all of the lamps will turn off. If the lamps are identical, each will get an equal share of the battery voltage and they will all have the same brightness. A series circuit is not practical for domestic lighting because if one of the bulbs blow, all of the other lamps will turn off because of the break in the circuit.
In a parallel circuit, there are points where the current is split to take two or more routes. If the lamps in a a parallel circuit are identical, the current will divide equally. Mains sockets and mains lights in homes are wired in parallel because each socket receives the full mains voltage. If a lamp should blow, all the others will continue to
2.9: Understand that the current in a series circuit depends on the applied voltage and the number and nature of other components
The current in a series circuit is the same in all parts of the circuit. It it worked out using the relationship between current, voltage, and resistance. The current received by the separate components in the circuit is the total of the voltage received divided by the resistances of all of the components.
The current in a series circuit is the same in all parts of the circuit. It it worked out using the relationship between current, voltage, and resistance. The current received by the separate components in the circuit is the total of the voltage received divided by the resistances of all of the components.
2.10: Describe how current varies with voltage in wires, resistors, metal filament lamps and diodes, and how this can be investigated experimentally
The relationship between current, resistance and voltage is defined by Ohm's Law. It can be shown by a simple equation:
I = v / r
Current = voltage / resistance
In the experiment shown on the left, more batteries can be added in order to vary the voltage. The resistance in the variable resistor can be changed and different values can be used to plug in to the formula.
The relationship between current, resistance and voltage is defined by Ohm's Law. It can be shown by a simple equation:
I = v / r
Current = voltage / resistance
In the experiment shown on the left, more batteries can be added in order to vary the voltage. The resistance in the variable resistor can be changed and different values can be used to plug in to the formula.
2.11: Describe the qualitative effect of changing resistance on the current in a circuit
Increasing the resistance will decrease the current. This can be achieved by adding more components or components with higher resistance. Decreasing the resistance will increase the current. This can be achieved by removing components or if components with higher resistance are replaced by those with lower resistance.
Increasing the resistance will decrease the current. This can be achieved by adding more components or components with higher resistance. Decreasing the resistance will increase the current. This can be achieved by removing components or if components with higher resistance are replaced by those with lower resistance.
2.12: Describe the qualitative variation of resistance of LDRs with illumination and of thermistors with temperature
If light is shone onto an LDR, the resistance decreases because electrons are freer to move around. The higher the illumination, the lower the resistance. If the temperature gets warmer, the resistance in the thermistor gets lower because the increased heat energy gives the electrons more energy to move around.
If light is shone onto an LDR, the resistance decreases because electrons are freer to move around. The higher the illumination, the lower the resistance. If the temperature gets warmer, the resistance in the thermistor gets lower because the increased heat energy gives the electrons more energy to move around.
2.13: Know that lamps and LEDs can be used to indicate the presence of a current in a circuit
Current is the flow of electrons. If a lamp or LED is connected to a complete circuit, it can be used to indicate the presence of a current; if the lamp or LED lights up, it shows that current is present. If the lamp or LED does not light up, there still may be current, but the other components may have too much resistance for enough current to power the lamp or LED, or the voltage of the cell may not be high enough.
Current is the flow of electrons. If a lamp or LED is connected to a complete circuit, it can be used to indicate the presence of a current; if the lamp or LED lights up, it shows that current is present. If the lamp or LED does not light up, there still may be current, but the other components may have too much resistance for enough current to power the lamp or LED, or the voltage of the cell may not be high enough.
2.14: Know and use the relationship between voltage, current and resistance
Voltage = current x resistance
V = I x R
Voltage = current x resistance
V = I x R
2.15: Understand that current is the rate of flow of charge
Current is the rate of flow of charge. This means that it is how many coulombs flow in a period of time.
Current is the rate of flow of charge. This means that it is how many coulombs flow in a period of time.
2.16: Know and use the relationship between charge, current and time
Charge = current x time
Q = I x t
Charge = current x time
Q = I x t
2.17: Know that electric current in solid metallic conductors is a flow of negatively charged electrons
When metals are charged, the atoms inside them usually turn into anions. This means that they are negatively charged because they have more electrons than protons. Electrons usually flow through solid metallic conductors.
When metals are charged, the atoms inside them usually turn into anions. This means that they are negatively charged because they have more electrons than protons. Electrons usually flow through solid metallic conductors.
2.18: Understand that the volt is the energy transferred per unit of charge passed and that the volt is a joule per coulomb
A volt is the energy transferred per unit of charge (joule per coulomb).
A volt is the energy transferred per unit of charge (joule per coulomb).
d) Electric charge
2.19: Identify common materials which are electric conductors or insulators, including metals and plastics
Materials that conduct electricity are called conductors. They are usually metallic, for example, copper. Materials that do not conduct electricity are called insulators. These are usually non-metallic, for example, rubber and many types of plastic.
Materials that conduct electricity are called conductors. They are usually metallic, for example, copper. Materials that do not conduct electricity are called insulators. These are usually non-metallic, for example, rubber and many types of plastic.
2.20: Describe experiments to investigate how insulating materials can be charged by friction
Acetate rods can be easily charged by rubbing them with a dry cloth. When rubbing two materials together some electrons are torn from the surface of one of the materials and transferred to the other. The material which loses electrons is positively charged and the material that gains electrons becomes negatively charged.
Acetate rods can be easily charged by rubbing them with a dry cloth. When rubbing two materials together some electrons are torn from the surface of one of the materials and transferred to the other. The material which loses electrons is positively charged and the material that gains electrons becomes negatively charged.
2.21: Explain that positive and negative electrostatic charges are produced and materials by the loss and gain of electrons
If a material gains electrons, it obtains more negatively charged particles and therefore has a negative charge. If a material loses electrons, it loses negatively charged particles and therefore has more protons than electrons which make it positively charged.
If a material gains electrons, it obtains more negatively charged particles and therefore has a negative charge. If a material loses electrons, it loses negatively charged particles and therefore has more protons than electrons which make it positively charged.
2.22: Understand that there are forces of attraction between unlike charges and forces of repulsion between like charges
There are forces of attraction between unlike charges and forces of repulsion between like charges. This can be demonstrated using two magnets. If you push the positive and negative end of two magnets together, they will attract because positive and negative are unlike charges. However, if you try to push the negative ends of two magnets together, they will repulse each other because negative and negative are unlike charges. The same will be true if the two positive ends are pushed together.
There are forces of attraction between unlike charges and forces of repulsion between like charges. This can be demonstrated using two magnets. If you push the positive and negative end of two magnets together, they will attract because positive and negative are unlike charges. However, if you try to push the negative ends of two magnets together, they will repulse each other because negative and negative are unlike charges. The same will be true if the two positive ends are pushed together.
2.23: Explain electrostatic phenomena in terms of movement of electrons
Electrostatic phenomena is an event where static electricity has a specific effect: for example a static shock. Electrons move from one material to another, and the negatively charged material looks for a way to earth its charge, for example, if your hand comes into contact with it, it earths its charge and you receive a small shock.
Electrostatic phenomena is an event where static electricity has a specific effect: for example a static shock. Electrons move from one material to another, and the negatively charged material looks for a way to earth its charge, for example, if your hand comes into contact with it, it earths its charge and you receive a small shock.
2.24: Explain the potential dangers of electrostatic charges
Electric shocks
Cars can become charged with static electricity, particularly on dry days, and can give electric shocks when someone comes into contact with the car.
Fuel tankers and aircraft
It is possible for static charge to build up on aircraft while they are flying and this may cause the fuel to ignite while the aircraft is refueling on the ground. This is prevented by ensuring that the plane is earthed when it reaches the ground in order to discharge it.
Computer chips
Workers handling electric components such as computer chips have to take care not to become statically charged as this may destroy expensive components. They have to wear earthing straps and work on earthed metal benches to prevent this.
Electric shocks
Cars can become charged with static electricity, particularly on dry days, and can give electric shocks when someone comes into contact with the car.
Fuel tankers and aircraft
It is possible for static charge to build up on aircraft while they are flying and this may cause the fuel to ignite while the aircraft is refueling on the ground. This is prevented by ensuring that the plane is earthed when it reaches the ground in order to discharge it.
Computer chips
Workers handling electric components such as computer chips have to take care not to become statically charged as this may destroy expensive components. They have to wear earthing straps and work on earthed metal benches to prevent this.
2.25: Explain some uses of electrostatic charges
Inkjet printers
Charging ink droplets in inkjet printers allows the droplets to be directed to particular places on the paper by deflecting them between charged plates
Photocopiers
A statically charged drum is exposed to light which is reflected from the document to be copied, which discharges the drum everywhere except where the dark print does not reflect light. The charged parts of the drum attract the toner which is transferred to the printing paper. The paper is heated to bond the toner particles to it.
Paint spraying
Tiny droplets of paint are statically charted and the object to be painted is connected to a supply of the opposite charge. This causes the paint droplets to be attracted to the object being painted and the amount of paint wasted is reduced since the opposite charges attract. This can also be used to paint obscure corners.
Electrostatic precipitators
Small particles of soot and other dust produces when burning waste materials are statically charged and then passed through a highly charged grid which attracts the dust particles, therefore stopping them from escaping into the atmosphere.
Inkjet printers
Charging ink droplets in inkjet printers allows the droplets to be directed to particular places on the paper by deflecting them between charged plates
Photocopiers
A statically charged drum is exposed to light which is reflected from the document to be copied, which discharges the drum everywhere except where the dark print does not reflect light. The charged parts of the drum attract the toner which is transferred to the printing paper. The paper is heated to bond the toner particles to it.
Paint spraying
Tiny droplets of paint are statically charted and the object to be painted is connected to a supply of the opposite charge. This causes the paint droplets to be attracted to the object being painted and the amount of paint wasted is reduced since the opposite charges attract. This can also be used to paint obscure corners.
Electrostatic precipitators
Small particles of soot and other dust produces when burning waste materials are statically charged and then passed through a highly charged grid which attracts the dust particles, therefore stopping them from escaping into the atmosphere.