Physics OCR AS Key Terms

Key terms and definitions for OCR Physics AS

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Absorption line spectrum ­ A dark line of a unique wavelength seen in a continuous spectrum
Acceleration ­ The rate of change of an object's velocity. Unit = ms-2
Ampere ­ the unit of electric current (A)
Amplitude ­ The maximum displacement of a particle from its equilibrium position
Antinode ­ A point on a stationary wave with maximum amplitude
Average speed ­ the total distance travelled by an object divided by the total time taken
Braking distance ­ the distance travelled by a vehicle from the moment when the brakes are
applied until the vehicle comes to rest
Brittle ­ describes a material that shows no plastic deformation and breaks just beyond its elastic
Centre of gravity ­ the point where the entire weight of an object appears to act
Charge carrier ­ any charged particles, such as electrons, responsible for a current
Coherent ­ two sources are coherent when they emit waves with a constant phase difference
Components (of a vector) ­ the magnitudes of a vector quantity in two perpendicular directions
Compression ­ a region in a sound wave where the air pressure is greater than its mean value
Compressive ­ a force that squeezes an object
Constructive interference ­ when two wave have no half wavelength phase difference, construct to
give increased amplitude, maxima
Coulomb ­ the unit of electrical charge. A charge of 1C passes a point when a current of 1A flows for
1s. 1C = 1As
Density ­ the mass per unit volume of a material.
Destructive interference ­ when two waves cancel to give reduced amplitude
Diffraction ­ the spreading of a wave when it passes through a gap or past the edge of an object
Dispersion ­ the splitting of light into its different wavelengths

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Displacement ­ the distance moved by an object in a particular direction (measured from a fixed
starting point)
Ductile ­ describes a material that can easily be drawn into wires (e.g.…read more

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Equilibrium ­ an object in equilibrium is either at rest or travelling with a constant velocity because
the net force on it is zero
Extension ­ the change in length of a material from its original length
Force constant ­ the ratio of force to extension for a spring or a wire. Unit = Nm-1
Frequency ­ the number of oscillations of a particle per unit time.…read more

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Kinetic energy ­ energy of an object due to its motion
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 conveys the conservation of charge
Kirchhoff's second law ­ the sum of the e.m.f.s round a loop in a circuit is equal to the sum of p.d.…read more

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Plastic deformation ­ the deformation of a material beyond the elastic limit
Potential difference (p.d.) ­ the energy lost per unit charge by charges passing through a
component. Unit = JC-1 or volt (V)
Potential divider ­ a circuit in which two or more components are connected in series to a supply.
The output voltage from the circuit is taken across one of the components
Power ­ the rate at which energy is transferred or the rate at which work is done.…read more

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Semiconductor diode ­ and electrical component made from a semiconductor material (e.g. silicon)
that only conducts in one direction. A diode in `reverse bias' has an infinite resistance
Series ­ when components are connected end-to-end in a circuit
Speed ­ the rate of change of the distance moved by an object.
Unit = ms-1
Stationary wave ­ a wave pattern produces when two progressive waves of the same frequency
travelling in opposite directions combine. It is characterised by nodes and antinodes.…read more

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Transverse waves ­ a wave in which the oscillation is at right angles to the direction in which the
wave travels
Triangle of forces ­ a closed triangle drawn for an object in equilibrium.…read more


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