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3.5 Electricity

6 dot points across 6 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

How do current, voltage and resistance combine in series and parallel circuits?

Combining resistors in series and parallel, the application of Kirchhoff's two laws, the conservation of charge and energy in circuits, and power dissipation given by P = VI, P = I squared R and P = V squared over R.
A focused answer to AQA A-Level Physics 3.5.1.4, covering the rules for combining resistors in series and parallel, the application of Kirchhoff's two laws, conservation of charge and energy in circuits, and the three equations for electrical power dissipation.
10 min answer →

What is electric current, and how is it linked to charge and the motion of carriers?

Electric current as the rate of flow of charge, the equation Q = It, charge carriers and number density, the equation I = nAvq for current, and Kirchhoff's first law as conservation of charge.
A focused answer to AQA A-Level Physics 3.5.1.1, covering electric current as the rate of flow of charge, the equation Q = It, charge carriers and number density, the equation I = nAvq, and Kirchhoff's first law as a statement of conservation of charge.
9 min answer →

How does current vary with potential difference for different components?

The definition of potential difference and resistance, Ohm's law, the I-V characteristics of an ohmic conductor, a filament lamp and a diode, and how the resistance of a thermistor and LDR varies.
A focused answer to AQA A-Level Physics 3.5.1.2, covering potential difference and resistance, Ohm's law, the current-voltage characteristics of an ohmic conductor, a filament lamp and a diode, and how the resistance of a thermistor and a light-dependent resistor changes.
10 min answer →

Why is the voltage across a battery's terminals less than its rated value when it supplies current?

Electromotive force as energy per unit charge, internal resistance, the equations linking EMF, terminal potential difference and lost volts, and measuring EMF and internal resistance experimentally.
A focused answer to AQA A-Level Physics 3.5.1.6, covering electromotive force as energy transferred per unit charge, internal resistance, the equations linking EMF, terminal potential difference and lost volts, and the experiment to measure EMF and internal resistance.
10 min answer →

How can we use resistors to supply a chosen fraction of a source voltage?

The potential divider as a way of producing a required potential difference, the divider equation, the use of variable resistors and potentiometers, and divider circuits using thermistors and LDRs as sensors.
A focused answer to AQA A-Level Physics 3.5.1.5, covering the potential divider as a way of supplying a chosen potential difference, the divider equation, the use of variable resistors and potentiometers, and sensing circuits built with thermistors and light-dependent resistors.
9 min answer →

What property of a material determines how strongly it resists current?

Resistivity and the equation R = rho L / A, the effect of length and cross-sectional area on resistance, how resistivity varies with temperature for a metal, and superconductivity and its uses.
A focused answer to AQA A-Level Physics 3.5.1.3, covering resistivity and the equation R = rho L / A, the effect of length and cross-sectional area on resistance, how the resistivity of a metal varies with temperature, and superconductivity with its applications.
9 min answer →