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3.7 Fields and their consequences

10 dot points across 10 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

How do we describe alternating current, and why are transformers essential to the power grid?

Sinusoidal alternating current and voltage, peak and root mean square values, the oscilloscope, the transformer equation, transformer efficiency and the transmission of electrical power.
A focused answer to AQA A-Level Physics 3.7.5.5 and 3.7.5.6, covering sinusoidal alternating current, peak and rms values, the oscilloscope, the transformer equation, transformer efficiency and the transmission of electrical power.
10 min answer →

How does a capacitor store charge and energy, and what limits how much it can hold?

The definition of capacitance, the energy stored on a capacitor, the effect of a dielectric and relative permittivity, and parallel plate capacitors.
A focused answer to AQA A-Level Physics 3.7.4, covering the definition of capacitance, the energy stored by a capacitor, the role of dielectrics and relative permittivity, and the parallel plate capacitor.
9 min answer →

How does the charge on a capacitor change with time as it charges or discharges through a resistor?

Exponential charge and discharge of a capacitor through a resistor, the time constant, and graphical and logarithmic analysis of the decay.
A focused answer to AQA A-Level Physics 3.7.4.4, covering the exponential charge and discharge of a capacitor through a resistor, the time constant RC, half-life of decay, and analysis using log-linear graphs.
10 min answer →

How do charged objects exert forces on one another, and how do gravitational and electric fields compare?

Coulomb's law, electric field strength as force per unit charge, the radial field of a point charge, uniform fields between plates, and the motion of charged particles in uniform fields.
A focused answer to AQA A-Level Physics 3.7.3, covering Coulomb's law, electric field strength as force per unit charge, radial and uniform fields, the comparison with gravitational fields, and the motion of charged particles in a uniform field.
10 min answer →

How much work is needed to move a charge through an electric field, and how does this compare with gravity?

Absolute electric potential and potential energy in a radial field, the potential gradient, equipotentials, and the work done moving a charge.
A focused answer to AQA A-Level Physics 3.7.3.3, covering absolute electric potential in a radial field, electric potential energy, the potential gradient and its link to field strength, equipotentials, and the work done moving a charge.
9 min answer →

How does a changing magnetic field generate an electromotive force?

Magnetic flux and flux linkage, Faraday's law and Lenz's law, the emf induced in a moving conductor, and the emf induced in a rotating coil.
A focused answer to AQA A-Level Physics 3.7.5.4, covering magnetic flux and flux linkage, Faraday's law and Lenz's law, the emf induced in a conductor moving through a field, and the emf produced by a rotating coil.
10 min answer →

How can a mass exert a force on another mass across empty space?

The concept of a force field, Newton's law of gravitation, gravitational field strength as a vector, and the radial and uniform field models.
A focused answer to AQA A-Level Physics 3.7.2, covering the concept of a force field, Newton's law of gravitation, gravitational field strength g as force per unit mass, and the radial and near-uniform field models.
9 min answer →

How much energy does it take to move a mass within a gravitational field?

Gravitational potential and potential energy in a radial field, the potential gradient, equipotential surfaces, and the work done moving a mass between points.
A focused answer to AQA A-Level Physics 3.7.2.3, covering gravitational potential in a radial field, gravitational potential energy, the potential gradient and its link to field strength, equipotential surfaces, and the work done moving a mass.
9 min answer →

What force does a magnetic field exert on a current or a moving charge, and why does it cause circular motion?

Magnetic flux density, the force on a current-carrying conductor, the force on a moving charge, Fleming's left hand rule, and the circular motion of charged particles.
A focused answer to AQA A-Level Physics 3.7.5.1, covering magnetic flux density, the force on a current-carrying conductor, Fleming's left hand rule, the force on a moving charge, and the resulting circular motion of charged particles.
9 min answer →

What keeps a satellite in orbit, and why do geostationary satellites sit at one fixed height?

Orbital motion under gravity, the link to centripetal force, Kepler's third law, the energy of an orbiting body, and synchronous and geostationary orbits.
A focused answer to AQA A-Level Physics 3.7.2.4, covering orbital motion under gravity, the link between gravitational and centripetal force, Kepler's third law, orbital energy, and synchronous and geostationary satellites.
10 min answer →