Sensing | OCR A-Level Physics B (Advancing Physics) (H557)
Sensing
- 175 questions
- 12 subtopics
- The physics content, examined on all three papers
- Component 01, Component 02 and Component 03
Sensing is examined in all three written papers — the specification states that Components 01, 02 and 03 each assess content from across all the teaching modules, so nothing is confined to one paper.
It covers current and the flow of charge, potential difference, e.m.f. and energy transfer, resistance, conductance and Ohm's law, series and parallel combinations, power and energy in electric circuits, internal resistance and e.m.f., Kirchhoff's laws and conservation in circuits, resistivity and conductivity, charge carrier number density in metals, semiconductors and insulators, current-potential difference characteristics and circuit components, the potential divider and sensing circuits and calibration.
Sample questions from Sensing
Answer each one closed book first, then open the answer.
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Current and the flow of charge
Define the coulomb.
Show the answer
One coulomb is the charge that passes a point when a current of one ampere flows for one second. -
Potential difference, e.m.f. and energy transfer
Explain why the e.m.f. of a cell is greater than the potential difference across its terminals when it delivers a current.
Show the answer
Some of the energy given to each coulomb is transferred inside the cell in driving the charge through its own internal resistance. -
Series and parallel combinations
Calculate the combined resistance of 4.0 Ω and 6.0 Ω in parallel.
Show the answer
The conductances add to 0.25 + 0.167 = 0.417 S, so the resistance is 2.4 Ω. -
Power and energy in electric circuits
Explain why electrical power is transmitted at very high voltage.
Show the answer
For a given power the current is much smaller, and the power wasted in the line resistance is proportional to the square of the current, so the losses fall sharply. -
Kirchhoff's laws and conservation in circuits
Which conservation principle does Kirchhoff's second law express?
Show the answer
It expresses the conservation of energy. -
Resistivity and conductivity
Describe how to determine the resistivity of a metal in wire form.
Show the answer
Measure the diameter with a micrometer at several places to find the cross-sectional area, measure the resistance for a range of lengths with a voltmeter and ammeter, plot resistance against length, and multiply the gradient by the area. -
Current-potential difference characteristics and circuit components
Describe the current–potential difference characteristic of a filament lamp.
Show the answer
It passes through the origin but curves towards the potential difference axis as the current rises, because the filament heats and its resistance increases. -
The potential divider
Why should the resistances in a potential divider not be made too small?
Show the answer
A large current then flows continuously through the divider, wasting power and heating the resistors.
The 12 subtopics
One subtopic is one session. Work down the list.
| Subtopic | What it covers | Questions |
|---|---|---|
| Current and the flow of charge | Recall questions on current as the rate of flow of charge, I = ΔQ/Δt, the coulomb, charge carriers in metals and electrolytes, counting electrons, conventional current, the same current around a series circuit, why a lamp lights at once, I = nAvq and drift speed in a narrowing wire, and why current is a scalar. | 14 |
| Potential difference, e.m.f. and energy transfer | Recall questions on defining potential difference, the volt and e.m.f., the difference between e.m.f. and potential difference, energy transferred per coulomb, and why a voltmeter must have a very high resistance. | 15 |
| Resistance, conductance and Ohm's law | Recall questions on resistance and conductance and their units, G = 1/R, Ohm's law and ohmic conductors, the ohm, why metal resistance rises and thermistor resistance falls when heated, the current–potential difference graphs of a filament lamp and a diode, and when conductance is more convenient than resistance. | 15 |
| Series and parallel combinations | Recall questions on combining resistances and conductances in series and in parallel, why a parallel combination has less resistance than its smallest branch, calculating combined resistances and branch currents, mixed series and parallel networks, current dividing in inverse proportion to resistance, and why household appliances are wired in parallel. | 15 |
| Power and energy in electric circuits | Recall questions on P = IV, P = I²R and P = V²/R, the watt, energy transferred W = VIt, why a resistor heats up, heater, battery and kettle calculations, high-voltage transmission, identical lamps in series, the safe current for a rated resistor, and why a filament glows while its leads stay cool. | 14 |
| Internal resistance and e.m.f. | Recall questions on the internal resistance of a source, terminal potential difference and lost volts, finding internal resistance from a graph, maximum power transfer, and why car batteries need very low internal resistance. | 15 |
| Kirchhoff's laws and conservation in circuits | Recall questions on Kirchhoff's first and second laws and the conservation of charge and energy they express, finding an unknown branch current and potential difference, why charge does not build up at a junction, signs around a loop, a cell with internal resistance, lamps in parallel, and why the laws hold in any network. | 12 |
| Resistivity and conductivity | Recall questions on R = ρL/A and G = σA/L, the units of resistivity and conductivity, σ = 1/ρ, how length and thickness affect resistance, a copper wire's resistance and conductivity, measuring the resistivity of a wire, measuring its diameter and keeping the current small, stretching a wire, and typical resistivities of conductors and insulators. | 15 |
| Charge carrier number density in metals, semiconductors and insulators | Recall questions on the number density of charge carriers in metals, semiconductors and insulators, how heating changes the conductance of a semiconductor and a metal, light-dependent resistors, calculating n = I/(Avq) for copper, tiny drift speeds, why thermistors are made from semiconductors, and insulators at very high temperatures. | 13 |
| Current-potential difference characteristics and circuit components | Recall questions on obtaining a current–potential difference characteristic with a potential divider, ohmic lines, finding resistance from a curve rather than its gradient, filament lamp and diode characteristics, thermistor and metal wire temperature graphs, meter placement and self-heating, symbols for thermistors, light-dependent resistors, cells and batteries, reversed readings, and voltmeter current. | 16 |
| The potential divider | Recall questions on what a potential divider is, Vₒᵤₜ = Vᵢₙ × R₂/(R₁ + R₂), potential difference in proportion to resistance, calculating outputs and resistance ratios, the loading effect and how to minimise it, rotary potentiometers and uniform wires, raising the upper resistance, and why a divider beats a series resistor for outputs from zero. | 15 |
| Sensing circuits and calibration | Recall questions on sensors, how thermistors and light-dependent resistors respond, potential dividers whose output rises or falls with temperature, calculating outputs with thermistors and light-dependent resistors, the sensitivity of a sensing circuit and choosing its fixed resistor, calibrating a thermistor circuit and why it needs a curve, and response time, resolution and thermal capacity. | 16 |
How the guide is worked
Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.
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Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
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Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
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Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.
Read the full method, the return schedule and the research behind it.
Nearby topics
OCR A-Level Physics B (Advancing Physics) Active Recall Guide
Every topic, not just this one. 2,455 questions with their answers.