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)
2.04 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)
2.07 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