2 Electricity - iGCSE Physics Edexcel

2.1 use the following units: ampere (A), coulomb (C), joule (J), ohm (Ω), second (s), volt (V) and watt (W)
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● Damaged insulation - contact with the wire due to gaps in the insulation can cause an electric shock or pose a fire hazard by creating a short circuit.

● Overheating of cables - high currents passing through thin wire conductors cause the wires to heat up to very high temperatures which could melt the insulation and cause a fire.

● Damp conditions - water can conduct a current so wet electrical equipment can cause an electric shock.

Fuses and circuit breakers:
● A fuse is a thin piece of wire which overheats and melts if the current is too high, protecting the circuit. They have a current rating which should be slightly higher than the current used by the device in the circuit. The most common are 3A, 5A and 13A.

● Circuit breakers consist of an automatic electromagnet switch which breaks the circuit if the current rises over a certain value. This is better than a fuse as it can be reset and used again, and they operate faster. Earthing metal cases:

● Earth wires create a safe route for current to flow through in the case of a short circuit, preventing electric shocks.

● Earth wires have a very low resistance so a strong current surges through them which breaks the fuse and disconnects the appliance.

Double insulation:
● Appliances with double insulation have either plastic casings completely covering their electrical components, or have been designed so that the earth wire cannot touch the metal casing, preventing them from giving an electric shock.
Relationship between voltage and current can be different for different types of components and is shown by an IV graph

-Linear line
-Through the whole graph

Filament lamp
-Resistance increases with temperature
-Slight plateaus on the ending of both sides of curve

-Only allows current to pass in one direction
-Line at Y=0 until certain point
-Around halfway through, Y begins to increase in linear fashion
Set up a circuit with:
-Ammeter in series
-Voltmeter in parallel to component

Starting with a low voltage, slowly increase the voltage of the power supply over a range of settings (e.g. from 1V to 12V in 1 V intervals).
Record the readings on the ammeter and voltmeter as you do so.
Repeat the experiment 3 times and take an average.
2.10 describe the qualitative effect of changing resistance on the current in a circuit-V=IR -As the resistance increases in a circuit, the current will decrease.2.11 describe the qualitative variation of resistance of light-dependent resistors (LDRs) with illumination and of thermistors with temperatureLDR 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 circuitLamps and LEDs light up when a current passes through them. -LEDs are types of diodes: They only allow current to pass in one direction through them and will only light if the current passes in that direction2.13 know and use the relationship between voltage, current and resistance: voltage = current × resistance V = I × RPotential difference (V) = Current (A) x Resistance (Ω) V=IR2.14 know that current is the rate of flow of chargeThe current is the flow of charge passing a point in a circuit every second.2.15 know and use the relationship between charge, current and time: charge = current × time Q = I × tCharge (C) = Current (A) x Time (s) Q=IT2.16 know that electric current in solid metallic conductors is a flow of negatively charged electrons-In a metal, current is caused by a flow of delocalized electrons. -Electrons are negatively charged and flow from negative to positive. -Current, however, is still defined as going from positive to negative.2.17 understand why current is conserved at a junction in a circuit-Current may split in a parallel circuit -Splits at junctions, and recombines when paths meet again -No current has split yet before the junction2.18 know that the voltage across two components connected in parallel is the sameVoltage -Same in parallel -Shared in series2.19 calculate the currents, voltages and resistances of two resistive components connected in a series circuitWhen two or more components are connected in series: The current in each component is the same. The total voltage across the components is equal to the sum of individual voltages. The combined resistance of the components is equal to the sum of individual resistances2.20 know that: • voltage is the energy transferred per unit charge passed • the volt is a joule per coulomb.-Voltage is the amount of energy transferred by each unit of charge passing between two points in that circuit. -The volt (V), is the same as a joule per coulomb (J/C), energy per charge -Total amount of energy it loses is the same as the energy it gains when it passes through the power supply2.21 know and use the relationship between energy transferred, charge and voltage: energy transferred = charge × voltage E = Q × VEnergy Transferred (J) = charge (C) x Voltage (V) E = Q x V2.22P identify common materials that are electrical conductors or insulators, including metals and plastics2.23P practical: investigate how insulating materials can be charged by friction2.24P explain how positive and negative electrostatic charges are produced on materials by the loss and gain of electrons2.25P know that there are forces of attraction between unlike charges and forces of repulsion between like charges2.26P explain electrostatic phenomena in terms of the movement of electrons2.27P explain the potential dangers of electrostatic charges, e.g. when fuelling aircraft and tankers2.28P explain some uses of electrostatic charges, e.g. in photocopiers and inkjet printers