Q: What does IP Combined Science Notes (Lower Sec, Year 1-2): 10) Electricity & Magnetism Essentials cover? A: Analyse current, voltage, and resistance in circuits, and relate magnetic fields to practical applications.
Electrical and magnetic phenomena underpin everything from school lab circuits to train systems. Treat circuit diagrams and field lines with the same rigour as algebraic manipulation.
Learning targets
State charge conventions and apply Ohm's law V=IR.
Compare series and parallel circuits in terms of current, voltage, and resistance.
Calculate electrical power and energy consumption using P=VI and E=Pt
.
Describe magnetic field patterns around magnets and current-carrying conductors; explain electromagnet applications.
1. Current, voltage, and resistance
Quantity
Definition
Unit
Current (I)
Rate of flow of charge, I=tQ.
A
Voltage (V)
Energy transferred per unit charge.
V
Resistance (R)
Opposition to current flow, R=IV.
Ω
Worked example - Ohm's law
A resistor draws 0.35A when 5.6V is applied.
R=0.355.6=16,Ω.
If the voltage doubles and resistor obeys Ohm's law, current doubles to 0.70A.
2. Series vs parallel
Property
Series
Parallel
Current
Same through each component.
Splits; sum of branch currents equals total.
Voltage
Sum of component voltages equals supply.
Voltage across each branch equals supply.
Resistance
Add component resistances in a single loop.
Sum reciprocals of branch resistances, then invert.
Worked example - Parallel combination
Two resistors 120Ω and 180Ω in parallel.
Series rule: add each resistor value e.g.Rtotal=R1+R2+R3+R4.
Parallel rule: add reciprocals and invert e.g.1/Rtotal=1/R1+1/R2+1/R3+1/R4.
Total current =0.125,A, consistent with I=71.99.0.
3. Electrical power & safety
P=VI=I2R=RV2.
Household energy usage: E=Pt (convert to kWh).
Fuse rating slightly above normal operating current; earth wire provides low-resistance path for fault current.
Worked example - Energy cost
A 1.2kW heater runs for 3.5h.
E=1.2×3.5=4.2,kWh.
If cost is $0.26 per kWh, total cost =$1.09 (rounded to 2 d.p.).
4. Magnetism & electromagnetism
Magnetic field lines emerge from north pole, enter south pole.
Around straight current-carrying conductor: concentric circles; direction given by right-hand grip rule (thumb points conventional current, fingers curl in field direction).
Solenoids produce uniform fields similar to bar magnets; adding iron core strengthens field.
Applications
Electromagnets in relays: small current energises coil, closing switch in external circuit.
Electric bells: current magnetises core, attracting armature, breaking circuit to produce oscillations.
DC motors: force on current-carrying coil in magnetic field causes rotation (Fleming's left-hand rule).
Try it yourself
Sketch current and voltage distributions for three identical bulbs connected (a) in series, (b) in parallel to the same battery. Predict relative brightness.
A 240V appliance draws 5.0A. Determine required power rating and suggest a suitable fuse.
Describe how reversing current direction affects the magnetic field around a solenoid. Propose one lab method to demonstrate the reversal.
