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Electrical Power, Energy and Safety

Electrical power is $P=IV$ , and the energy transferred is $E=IVt$ . Electricity companies charge per kilowatt-hour: the energy used by a $1$ kW appliance in $1$ hour. Fuses and circuit breakers cut off the current if it gets too big; earthing a metal case makes a fault blow the fuse instead of electrocuting you.

Series and Parallel Circuits

In series, the current is the same everywhere, p.d.s add up to the supply, and resistances add. In parallel, each branch gets the full p.d., the branch currents add up to the total, and the combined resistance is less than any single branch. A potential divider shares the supply p.d. in the ratio of its resistances.

Energy Stored in a Capacitor

As a capacitor charges, each new bit of charge is pushed onto the plates against a rising p.d., so the p.d.–charge graph is a straight line through the origin. The energy stored is the area under it: $W=\tfrac12QV=\tfrac12CV^2=\dfrac{Q^2}{2C}$ . A battery charging a capacitor supplies $QV$ , but only half is stored; the other half is dissipated in the circuit resistance.

Logic Gates and Counters

Logic gates combine binary inputs: AND ( $A\cdot B$ ), OR ( $A+B$ ), NOT ( $\bar A$ ), NAND, NOR and XOR. Truth tables list every input combination ( $2^n$ rows). Sequential circuits remember: an astable produces a clock signal, and a binary counter counts its pulses; each stage halves the frequency.

Signals, Sampling and LC Filters

An analogue signal varies continuously; a digital one has discrete levels. Digitising samples the signal at least twice per cycle of its highest frequency, and an $n$ -bit sample has $2^n$ levels; bit rate $=$ samples per second $\times$ bits per sample. An LC circuit resonates at $f_0=\frac1{2\pi\sqrt{LC}}$ , picking out one band of frequencies; its sharpness is $Q=\frac{f_0}{f_B}$ .

The Heart and Circulation

Mammals have a double circulation: blood passes through the heart twice per circuit, once to the lungs (pulmonary) and once to the body (systemic), keeping body pressure high. Deoxygenated blood enters the right atrium from the vena cava, passes to the right ventricle, and is pumped through the pulmonary artery to the lungs. Oxygenated blood returns in the pulmonary vein to the left atrium, then the left ventricle, which pumps it out through the aorta. Valves stop backflow. The left ventricle wall is thickest. Coronary heart disease happens when fatty deposits block the coronary arteries.

Syllabus topics

Topic	Board	Paper	Lesson
Series and parallel circuits	Cambridge 5054	Multiple Choice	Available
Series and parallel circuits	Cambridge 5054	Theory	Available
Series and parallel circuits	Cambridge 0625	Extended	Available
Series and parallel circuits	Cambridge 0625	Core	Available
Series and parallel circuits	Edexcel 4PH1	Paper 1 (core content)	Available
Series and parallel circuits	Edexcel 4PH1	Paper 2 (all content)	Available
D.C. circuits	Cambridge 9702	Multiple Choice	Planned
D.C. circuits	Cambridge 9702	AS Level Structured Questions	Planned
Electric circuits	Edexcel YPH11	Unit 2: Waves and Electricity	Planned

Questions

ID	Question	Topic	Marks	Difficulty
SA-5054-EL2-004	A 6.0 V battery moves 5.0 C of charge round a circuit. Calculate the energy it transfers.…	Physics: charge, current and potential difference Electromotive force and potential difference	2	L1 Foundation
SA-5054-EL4-001	Calculate the combined resistance of 4.0 Ω and 6.0 Ω resistors in series.…	Physics: series and parallel circuits Series circuits and combined resistance	1	L1 Foundation
SA-5054-EL4-002	4.0 Ω and 6.0 Ω resistors are connected in series to a 12 V supply. Calculate the current.…	Physics: series and parallel circuits Series circuits and combined resistance	2	L1 Foundation
SA-5054-EL4-006	Two resistors are connected in parallel. Their combined resistance is…	Physics: series and parallel circuits Parallel circuits, potential dividers and sensors	1	L1 Foundation
SA-5054-EL4-009	Three 1.5 V cells are connected in series, all facing the same way. Calculate the total e.m.f.…	Physics: series and parallel circuits Series circuits and combined resistance	1	L1 Foundation
SA-5054-EL4-010	Three lamps are connected in parallel across a 6.0 V supply. State the p.d. across each lamp.…	Physics: series and parallel circuits Parallel circuits, potential dividers and sensors	1	L1 Foundation
SA-5054-EL4-012	An advantage of wiring house lights in parallel is that…	Physics: series and parallel circuits Parallel circuits, potential dividers and sensors	1	L1 Foundation
SA-5054-EL6-005	An a.c. generator is connected to the external circuit by…	Physics: electromagnetic induction and the a.c. generator The a.c. generator and using an oscilloscope	1	L1 Foundation
SA-9702-DC1-006	A high-resistance voltmeter connected directly across a cell with no other circuit reads approximately…	Physics: e.m.f. and internal resistance E.m.f., terminal p.d. and internal resistance, E = I(R + r)	1	L1 Foundation
SA-9702-CA2-010	A battery of e.m.f. 9.0 V charges a capacitor until it holds 2.0 mC. Calculate the energy dissipated in the circuit resistance, in mJ.…	Physics: energy stored in a capacitor W = ½QV = ½CV² = Q²/2C	1	L1 Foundation
SA-9702-CA3-010	Doubling the resistance in a discharging RC circuit…	Physics: discharging a capacitor and the time constant The time constant τ = RC and its meaning	1	L1 Foundation
SA-5054-EL4-005	The total current from a supply is 3.0 A. It splits into two parallel branches. One branch carries 1.2 A. Calculate the current in the other branch.…	Physics: series and parallel circuits Parallel circuits, potential dividers and sensors	1	L1 Foundation
SA-9702-AC2-004	The smoothing capacitor in a rectifier circuit is connected…	Physics: rectification and smoothing Smoothing with a capacitor and the effect of RC on ripple	1	L1 Foundation
SA-PX-DL-002	State the number of rows in a truth table for a circuit with 3 inputs.…	Physics: digital logic and counters Logic gates and truth tables	1	L1 Foundation
SA-9702-DC2-003	In the circuit of the previous question (2.0 A from the supply), calculate the current in the 3.0 Ω resistor.…	Physics: Kirchhoff's laws and combining resistors Kirchhoff's first and second laws as conservation of charge and energy	1	L2 Standard