A-Level Physics · Topic 7
Fields: gravitational, electric and magnetic: every key term you need (+ practice quiz)
16 flashcard terms for A-Level Physics Topic 7, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 8-question quiz — free, no account needed.
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Gravitational field strength Force per unit mass at a point, measured in newtons per kilogram. Numerically equal to free-fall acceleration.
Newton's law of gravitation The attractive force between two point masses is proportional to their product and inversely proportional to the square of their separation.
Gravitational potential Work done per unit mass bringing a mass from infinity to a point. Always negative, since gravity is only attractive.
Escape velocity The minimum launch speed for an object to reach infinity with zero kinetic energy. Independent of the object's mass.
Geostationary orbit A 24-hour equatorial orbit, so the satellite stays above one point on Earth. Used for communications.
Kepler's third law The square of the orbital period is proportional to the cube of the orbital radius — derivable by equating gravitational and centripetal force.
Coulomb's law The force between two point charges is proportional to their product and inversely proportional to the square of their separation.
Electric field strength Force per unit positive charge, in newtons per coulomb. Uniform between parallel plates, radial around a point charge.
Comparing gravitational and electric fields Both obey inverse square laws, but gravity is only attractive while electric fields can attract or repel, and gravity is vastly weaker.
Capacitance Charge stored per unit potential difference, measured in farads. Depends on plate area, separation and the dielectric.
Energy stored in a capacitor The area under a charge-voltage graph, equal to half the charge times the potential difference.
Capacitor time constant Resistance times capacitance. After this time, charge has fallen to about 37 per cent of its initial value.
Magnetic flux density The strength of a magnetic field, measured in tesla. Defined from the force on a current-carrying conductor.
Fleming's left hand rule First finger field, second finger current, thumb motion — gives the direction of force on a current-carrying conductor.
Faraday's law Induced electromotive force is proportional to the rate of change of magnetic flux linkage.
Lenz's law The induced current opposes the change producing it. A direct consequence of conservation of energy.
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