Page 562 - Physics Coursebook 2015 (A level)

Cambridge International AS and A Level Physics
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kinetic energy Energy of an object due to its motion. kinetic theory of gases A model based on the microscopic
motion of atoms or molecules of a gas.
Kirchhoff ’s first law The sum of the currents entering any point (or junction) in a circuit is equal to the sum of the currents leaving that same point. This law represents the conservation of charge.
Kirchhoff ’s second law The sum of the e.m.f.s round a closed loop in a circuit is equal to the sum of the p.d.s in that same loop.
Larmor frequency The frequency of precession of a nucleus in an external magnetic field.
Lenz’s law An induced current or e.m.f. is in a direction so as to produce effects which oppose the change producing it.
lepton A sub-atomic particle which is not affected by the strong nuclear force.
light-dependent resistor (LDR) A resistor whose resistance decreases as the intensity of light falling on it increases.
light-emitting diode (LED) A semiconductor component that emits light when it conducts electricity.
linear momentum The product of an object’s mass and its velocity, p = mv. Momentum is a vector quantity.
longitudinal wave A wave in which the particles of the medium oscillate along the direction in which the wave travels.
lost volts The difference between the e.m.f. and the terminal p.d. in a circuit. It is equal to the voltage across the internal resistance.
magnetic field A force field in which a magnet, a wire carrying a current, or a moving charge experiences a force.
magnetic flux The product of magnetic flux density normal to a circuit and the cross-sectional area of the circuit. Unit: weber (Wb).
magnetic flux density The strength of a magnetic field. Magnetic flux density B is defined as:
B = F IL
where F is the force experienced by a conductor in the magnetic field, I is the current in the conductor and L is the length of the conductor in the magnetic field. (The conductor is at right angles to the field.)
magnetic flux linkage The product of magnetic flux and the number of turns. Unit: weber (Wb).
magnetic resonance imaging (MRI) A medical imaging technique which uses nuclear magnetic resonance.
mass A measure of the amount of matter within an object. Unit: kilogram (kg).
mass defect The difference between the total mass of the individual, separate nucleons and the mass of the nucleus.
mass excess the difference between the mass of a nuclide (in u) and its mass number.
mean drift velocity The average speed of a collection of charged particles when a current flows.
microwave link A communications system that uses a beam of radio waves in the microwave frequency range to transmit audio, data or video information.
modulation The process of using one waveform to alter the frequency, amplitude or phase of another waveform.
mole The amount of matter which contains 6.02 × 1023 particles.
moment The moment of a force about a point is the magnitude of the force, multiplied by the perpendicular distance of the point from the line of the force. Unit: N m.
monochromatic Describes light of a single frequency. natural frequency The unforced frequency of oscillation
of a freely oscillating object.
negative feedback The output of a system is used to oppose changes to the input of the system, with the result that the changes are reduced.
neutrino A lepton, released during beta-decay.
neutron number The number of neutrons in the nucleus
of an atom.
newton The force that will give a 1 kg mass an acceleration of 1 m s−2 in the direction of the force. 1 N = 1 kg m s−2.
Newton’s first law of motion An object will remain at rest or keep travelling at constant velocity unless it is acted on by a resultant force.
Newton’s law of gravitation Any two point masses attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of their separation.
Newton’s second law of motion The resultant force acting on an object is equal to the rate of change of its momentum. The resultant force and the change in momentum are in the same direction.
Newton’s third law of motion When two bodies interact, the forces they exert on each other are equal and opposite.
node A point on a stationary wave with zero amplitude.
noise
signal.
An unwanted random addition to a transmitted