A-level Physics₇₄₀₈

Simplified structure, behaviour and characteristics.

Drain, source and gate.

${\mathit{V}}_{\mathrm{DS}}$ , ${\mathit{V}}_{\mathit{GS}}$ , ${\mathit{I}}_{\mathit{DSS}}$ , and ${\mathit{V}}_{\mathit{th}}$

Use as a switch, use as a device with a very high input resistance.

Use in N-channel, enhancement mode only is required.

Characteristic curve showing zener breakdown voltage and typical minimum operating current.

Anode and cathode.

Use with a resistor as a constant voltage source.

Use to provide a reference voltage.

Use as a stabiliser is not required.

Characteristic curves and spectral response curves.

Use in photo-conductive mode as a detector in optical systems.

Use with scintillator to detect atomic particles.

Use as magnetic field sensor to monitor attitude.

Use in tachometer.

Principles of operation are not required.

Bits, bytes.

Analogue-to-digital conversion:

• sampling audio signals for transmission in digital form
• conversion of analogue signals into digital data using two voltage levels
• quantisation
• sampling rate
• effect of sampling rate and number of bits per sample on quality of conversion
• advantages and disadvantages of digital sampling
• process of recovery of original data from noisy signal
• effect of noise in communication systems.

Pulse code modulation.

Students should appreciate the use of a variety of sensors to collect analogue data.

The ability to carry out binary arithmetic is not required. Knowledge of binary numbers 1 to 10 is adequate.

Resonant frequency, ${\mathit{f}}_{\mathsf{0}}\mathsf{=}\frac{\mathsf{1}}{\mathsf{2}\mathrm{\pi }\sqrt[]{\mathit{L}\mathit{C}}}$

Only parallel resonance arrangements are required.

Analogy between LC circuit and mass–spring system.

Inductance as mass analogy.

Capacitance as spring analogy.

Derivation of the equation is not required.

Energy (voltage) response curve.

The response curve for current is not required.

$\mathit{Q}$ factor, $\mathit{Q}\mathsf{=}\frac{{\mathit{f}}_{\mathsf{0}}}{{\mathit{f}}_{\mathrm{B}}}$

${\mathit{f}}_{\mathrm{B}}$ is the bandwidth of the filter at the 50% energy points.

Operation and characteristics of an ideal operational amplifier:

• power supply and signal connections
• infinite open-loop gain
• infinite input resistance.

Open-loop transfer function for a real operational amplifier, ${\mathit{V}}_{\mathrm{out}}\mathsf{=}{\mathit{A}}_{\mathrm{O}\mathrm{L}}\mathsf{(}{\mathit{V}}_{\mathsf{+}}\mathsf{-}{\mathit{V}}_{\mathsf{-}}\mathsf{)}$

Use as a comparator.

The operational amplifier should be treated as an important system building block.

Derivation of $\mathit{ }\frac{{\mathit{V}}_{\mathrm{o}\mathrm{u}\mathrm{t}}}{{\mathit{V}}_{\mathrm{i}\mathrm{n}}}\mathsf{=}\mathsf{-}\frac{{\mathit{R}}_{\mathrm{f}}}{{\mathit{R}}_{\mathrm{i}\mathrm{n}}}$ , calculations.

Meaning of virtual earth, virtual-earth analysis.

$\frac{{\mathit{V}}_{\mathrm{o}\mathrm{u}\mathrm{t}}}{{\mathit{V}}_{\mathrm{i}\mathrm{n}}}\mathsf{=}\mathsf{1}\mathsf{+}\frac{{\mathit{R}}_{\mathrm{f}}}{{\mathit{R}}_{\mathrm{l}}}$

Derivation is not required.

${\mathit{V}}_{\mathrm{o}\mathrm{u}\mathrm{t}}\mathsf{=}\mathsf{-}{\mathit{R}}_{\mathrm{f}}\left(\frac{{\mathit{V}}_{\mathsf{1}}}{{\mathit{R}}_{\mathsf{1}}}\mathsf{+}\frac{{\mathit{V}}_{\mathsf{2}}}{{\mathit{R}}_{\mathsf{2}}}\mathsf{+}\frac{{\mathit{V}}_{\mathsf{3}}}{{\mathit{R}}_{\mathsf{3}}}\mathsf{+}\mathsf{\dots }\right)$

Difference amplifier configuration.

Derivation is not required.

${\mathit{V}}_{\mathrm{o}\mathrm{u}\mathrm{t}}\mathsf{=}\mathsf{(}{\mathit{V}}_{\mathsf{+}}\mathsf{-}{\mathit{V}}_{\mathsf{-}}\mathsf{)}\frac{{\mathit{R}}_{\mathrm{f}}}{{\mathit{R}}_{\mathrm{l}}}$

Derivation is not required.

Limitations of real operational amplifiers.

Frequency response curve.

$\mathit{g}\mathit{a}\mathit{i}\mathit{n}\mathit{ }\mathsf{\times }\mathit{b}\mathit{a}\mathit{n}\mathit{d}\mathit{w}\mathit{i}\mathit{d}\mathit{t}\mathit{h}\mathsf{=}\mathit{c}\mathit{o}\mathit{n}\mathit{s}\mathit{t}\mathit{a}\mathit{n}\mathit{t}$ for a given device.

Use of Boolean algebra related to truth tables and logic gates.

$\stackrel{\mathsf{-}}{\mathit{A}}\mathsf{=}\mathit{not}\mathit{ }\mathit{A}$

$\mathit{A}\mathsf{\bullet }\mathit{B}\mathsf{=}\mathit{A}\mathit{ }\mathit{and}\mathit{ }\mathit{B}$

$\mathit{A}\mathsf{+}\mathit{B}\mathsf{=}\mathit{A}\mathit{ }\mathit{or}\mathit{ }\mathit{B}$

Identification and use of AND, NAND, OR, NOR, NOT and EOR gates in combination in logic circuits.

Construction and deduction of a logic circuit from a truth table.

The gates should be treated as building blocks. The internal structure or circuit of the gates is not required.

Counting circuits:

• Binary counter
• BCD counter
• Johnson counter.

Inputs to the circuits, clock, reset, up/down.

Outputs from the circuits.

Modulo- $\mathit{n}$ counter from basic counter with the logic driving a reset pin.

The gates should be treated as building blocks. The internal structure or circuit of the gates is not required.

The astable as an oscillator to provide a clock pulse.

Clock (pulse) rate (frequency), pulse width, period, duty cycle, mark-to-space ratio.

Variation of running frequency using an external $\mathit{R}\mathit{C}$ network.

Knowledge of a particular circuit or a specific device (eg 555 chip) will not be required.

Communication systems, block diagram of 'real time' communication system.

Only the purpose of each stage is required.

Transmission-path media: metal wire, optic fibre, electromagnetic (radio, microwave).

Ground wave, refraction and reflection of sky waves, diffraction of long-wavelength radiation around the Earth’s surface.

Satellite systems and typical transmission frequencies.

Students should recognise that up- and down-links require different frequencies so that the receivers are not de-sensed.

Advantages and disadvantages of various transmission media. Students should consider data transmission rate, cost, and security issues.

Basic principles of time-division multiplexing.

Principles of modulation; bandwidth.

Carrier wave and information signal.

Details of modulation circuits for modulating a carrier signal with the information signal will not be required.

Graphical representation of both AM and FM modulated signals.

A detailed mathematical treatment is not required.

Students will be expected to identify the carrier frequency and the information frequency from a graph of the variation of signal voltage with time.

Bandwidth requirements of simple AM and FM:

$\mathit{b}\mathit{a}\mathit{n}\mathit{d}\mathit{w}\mathit{i}\mathit{d}\mathit{t}\mathit{h}\mathsf{=}\mathsf{2}{\mathit{f}}_{\mathrm{M}}$ for AM

$\mathit{b}\mathit{a}\mathit{n}\mathit{d}\mathit{w}\mathit{i}\mathit{d}\mathit{t}\mathit{h}\mathsf{=}\mathsf{2}\left(\mathrm{∆}\mathit{f}\mathsf{+}{\mathit{f}}_{\mathrm{M}}\right)$ for FM

Data capacity of a channel.

Comparison of bandwidth availability for various media.