2.01 use the following units: ampere (A), coulomb (C), joule (J), ohm (Ω), second (s), volt (V) and watt (W)
unit for:
current : Ampere (A)
charge : coulomb (C)
resistance : ohm (Ω)
time : second (s)
potential difference : volt (V)
power : watt (W)
2.02 understand how the use of insulation, double insulation, earthing, fuses and circuit breakers protects the device or user in a range of domestic appliances
Fuses Stop the flow of current by melting if the current is too high. So protecting sensitive components and people because if the components function at too higher temperature it can cause a fire.
Circuit breakers again break the circuit if current is too high.
Insulation and double insulation prevent people from touching exposed wires and getting shocks.
Earthing provides a low resistance path to the earth so if some one does come into contact with a current instead of flowing through them to the earth giving them a shock it flows through the earthing wire.
2.03 understand why a current in a resistor results in the electral transfer of energy and an increase in temperature, and how this can be used in a variety of domestic contexts
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Resistance causes transfer of electrical energy to heat energy. Some components are designed to have a high resistance to make sure this happens, for example electrical heaters that have lots of resistors to ensure a high resistance so a lot of heat is produced. |
2.04 know and use the relationship between power, current and voltage: and apply the relationship to the selection of appropriate fuses
power (w) = current (A) x voltage (V)
when looking at a circuit a component will be given a power and a voltage appropriate to run at then the current can be calculated so the rating of the fuse can be selected for slightly higher than that.
2.05 use the relationship between energy transferred, current, voltage and time: E= I × V × T
Energy (J) = potential difference (V) x current (A) x Time (s)
2.06 know the difference between mains electricity being alternating current (a.c.) and direct current (d.c.) being supplied by a cell or battery
AC is constantly changing magnitude and direction. AC is how mains electricity is produced from turbines.
DC is constant. And is produced from a battery and used in some sensitive components like in computing.
2.07 explain why a series or parallel circuit is more appropriate for particular applications, including domestic lighting
Advantages of parallel circuits:
- Components (e.g. bulbs) may be switched on/off independently.
- If one component breaks, current can still flow through the other parts of the circuit.
- Bulbs maintain a similar brightness.
Advantages of series circuits:
- Fewer wires, cheaper and easier to assemble.
- Uses less power
2.08 understand how the current in a series circuit depends on the applied voltage and the number and nature of other components
Notes on current:
- As voltage increases the current also increases.
- In general, the more components in a circuit, the lower the current.
2.09 describe how current varies with voltage in wires, resistors, metal filament lamps and diodes, and how to investigate this experimentally
in the bellow diagram the red box could represent a wire, a bulb, a resistor or a diode.
By changing the resistance of the variable resistor the graphs are reproduced.
2.10 describe the qualitative effect of changing resistance on the current in a circuit
Since V = IR, as you increase the resistance in a circuit, the current will decrease.
2.11 describe the qualitative variation of resistance of light-dependent resistors (LDRs) with illumination and thermistors with temperature
LDR
As illumination increases, resistance decreases
Thermistor
As temperature increases, resistance decreases.
2.12 know that lamps and LEDs can be used to indicate the presence of a current in a circuit
A lamp can be added to a circuit to check for a current. If current is flowing, the lamp will light up.
2.13 know and use the relationship between voltage, current and resistance: V = I × R
Potential difference (V) = Current (A) x Resistance (Ω)
2.14 know that current is the rate of flow of charge
current is rate of flow of charge so I=Q/t
2.15 know and use the relationship between charge, current and time: Q = I × t
Charge (C) = Current (A) x Time (s)
2.16 know that electric current in solid metallic conductors is a flow of negatively charged electrons
Electrons are negatively charged and free to flow in a metal so carry charge
2.17 understand why current is conserved at a junction in a circuit
At a junction current ‘splits’ to take both paths.
It comes back together when the paths meet again.
I1 = I2 + I3 +I4
2.19 calculate the currents, voltages and resistances of two resistive components connected in a series circuit
VT = V1 + V2
IT = I1 = I2
RT = R1 + R2
2.21 know and use the relationship between energy transferred, charge and voltage: E = Q × V
Energy Transferred (J) = charge (C) x Voltage (V)
2.22 identify common materials which are electrical conductors or insulators, including metals and plastics
Conducting Materials:
- Copper
- Aluminium
- Gold
- Silver
Will conduct electricity
Insulating Materials:
- Glass
- Air
- Plastic
- Rubber
- Wood
Will not conduct electricity
2.23 practical: investigate how insulating materials can be charged by friction
- Hold polythene rod and cloth next to up small pieces of paper one at a time, observe.
- Now rub the rod with the cloth
- Again hold close to small pieces of paper, observe.
- Turn on a tap so a thin stream of water is flowing
- Hold the rod about 1cm away from the water just below the nozzle, observe
- Repeat with different material rods and cloths
2.28 explain some uses of electrostatic charges, e.g. in photocopiers and inkjet printers
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Paper is charged negatively in certain regions. Then positively charged paint droplets are sprayed onto the paper and attracted to the negative regions of the paper giving the desired image. |