Electricity — Numerical Practice
Covers: I = Q/t, E = W/Q, V = W/Q, R = V/I, series/parallel resistance, P = IV, E = IVt, kWh cost, and transformers (Vp/Vs = Np/Ns, IpVp = IsVs, P = I²R). 30 questions — the most formula-dense topic in the syllabus.
A. Charge and Current
A charge of 15 C flows past a point in 3 s. Calculate the current.
A current of 2 A flows for 10 s. Calculate the charge that flows.
A charge of 50 C flows at a current of 4 A. Calculate the time taken.
A current of 0.5 A flows for 2 minutes. Calculate the charge that flows.
Explain the difference between the direction of conventional current and the direction of electron flow in a wire.
B. E.m.f., Potential Difference and Resistance
20 J of work moves 4 C of charge through a resistor. Calculate the potential difference.
A cell of e.m.f. 6 V moves 3 C of charge around a complete circuit. Calculate the work done.
A resistor has a p.d. of 12 V across it and a current of 3 A through it. Calculate its resistance.
A resistor of 15 Ω has a current of 0.4 A through it. Calculate the p.d. across it.
A resistor of 18 Ω has a p.d. of 9 V across it. Calculate the current through it.
Explain why a filament lamp’s resistance increases as it gets hotter, and describe the effect this has on its current-voltage graph.
C. Series and Parallel Circuits
Three resistors of 2 Ω, 5 Ω and 3 Ω are connected in series. Calculate the total resistance.
Two resistors of 8 Ω and 8 Ω are connected in parallel. Calculate the combined resistance.
Resistors of 6 Ω and 12 Ω are connected in parallel. Calculate the combined resistance.
Two 1.5 V cells are connected in series with a 5 Ω resistor. Assuming no internal resistance, calculate the current in the circuit.
A current of 5 A enters a junction in a parallel circuit and splits into two branches. One branch carries 2 A. Calculate the current in the other branch.
Explain one advantage of connecting household lamps in parallel rather than in series.
D. Electrical Power and Energy
A device draws 4 A from a 12 V supply. Calculate its power.
An appliance has a power of 1500 W and operates at 230 V. Calculate the current it draws.
Calculate the energy transferred by a 100 W device running for 5 minutes, in joules.
A 2 kW heater runs for 3 hours. Calculate the energy transferred in kWh, and the cost at $0.20 per kWh.
A device transfers 5000 J of energy in 25 s. Calculate its power.
Explain the difference between the joule and the kilowatt-hour, both units of energy.
E. Transformers and Power Transmission
A transformer has 100 turns on its primary coil and 500 turns on its secondary coil, with a primary voltage of 20 V. Calculate the secondary voltage, and state whether this is a step-up or step-down transformer.
A transformer has a primary voltage of 230 V and a secondary voltage of 11.5 V. Calculate the turns ratio Np:Ns (in simplest form), and state whether this is step-up or step-down.
A transformer has a primary current of 2 A and a primary voltage of 230 V. The secondary voltage is 4600 V. Assuming 100% efficiency, calculate the secondary current.
A transformer has 1000 turns on its primary coil, 100 turns on its secondary coil, and a primary current of 0.5 A. Assuming 100% efficiency, calculate the secondary current.
A cable of resistance 4 Ω carries a current of 2 A. Calculate the power lost as heat in the cable.
A power of 10000 W is transmitted along a cable of resistance 5 Ω, once at 1000 V (giving a current of 10 A) and once at 10000 V (giving a current of 1 A). Calculate the power lost as heat in each case, and compare them.
Explain, using P = I²R, why electricity is transmitted at high voltage over long distances.
F. Potential Dividers
Two resistors, 20 Ω and 30 Ω, are connected in series across a 10 V supply as a potential divider. Calculate the voltage across the 30 Ω resistor.
Two resistors, 40 Ω and 60 Ω, are connected in series across a 20 V supply as a potential divider. Calculate the voltage across the 60 Ω resistor.
In a potential divider, a 15 Ω resistor has 5 V across it. A second resistor of 25 Ω is in series with it. Use R₁/R₂ = V₁/V₂ to calculate the voltage across the 25 Ω resistor.
Explain the purpose of a potential divider circuit.
Mastery Test
A charge of 40 C flows past a point in 8 s. Calculate the current.
A current of 3 A flows for 15 s. Calculate the charge that flows.
60 J of work moves 12 C of charge through a component. Calculate the potential difference.
A component has a p.d. of 20 V across it and a current of 2.5 A. Calculate its resistance.
Three resistors of 4 Ω, 7 Ω and 9 Ω are connected in series. Calculate the total resistance.
Two resistors of 10 Ω and 10 Ω are connected in parallel. Calculate the combined resistance.
A device draws 6 A from a 220 V supply. Calculate its power.
A 250 W device runs for 40 s. Calculate the energy transferred.
A transformer has 300 turns on its primary coil, 60 on its secondary, and a primary voltage of 120 V. Calculate the secondary voltage, and state whether this is step-up or step-down.
A cable of resistance 2 Ω carries a current of 5 A. Calculate the power lost as heat.
Book a free trial class
Tell us a little about your requirement.