# ALL A2 PHYSICS DEFINITIONS (G484 + G485)

All **A2** definitions required for **OCR A** syllabus.

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- Created by: Ciarán
- Created on: 26-02-14 21:17

NEWTON’S FIRST LAW

When viewed in an inertial reference frame, an object either is at rest or moves at a constant velocity, unless acted upon by an external force.

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NEWTON’S SECOND LAW

Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object). F=Ma.

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NEWTON’S THIRD LAW

When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction to that of the first body.

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LINEAR MOMENTUM

The product of mass and velocity. Momentum is always conserved

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NET FORCE

Net force on a body as equal to rate of change of its momentum

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IMPULSE OF A FORCE

Ft=average force x time

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PERFECT ELASTIC COLLISION

Kinetic energy and momentum is conserved. No energy is dissipated as heat etc.

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INELASTIC COLLISION

Momentum is conserved but kinetic energy is not. Energy is converted into heat etc.

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RADIAN

Unit of angle or phase difference. One radian is the angle subtended at the centre of a circle by an arc of circumference that is equal in length to the radius of the circle. 2π=360°

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GRAVITATIONAL FIELD STRENGTH

Force per unit mass g=F/M

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GEOSTATIONARY ORBIT

Geostationary satellites orbit directly above the same point every 24 hours e.g. TV/satellite signals

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DISPLACEMENT

Distance of object from midpoint (m)

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AMPLITUDE

The maximum displacement from the equilibrium position (m)

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FREQUENCY

The number of oscillations per unit time (Hz)

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ANGULAR FREQUENCY

The frequency of a steadily recurring phenomenon expressed in radians per second. A frequency in hertz can be converted to an angular frequency by multiplying it by 2π.

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PHASE DIFFERENCE

A measure of the relationship between the pattern of vibration at two points. Two points that have the same pattern are in phase (0 phase difference).

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SIMPLE HARMONIC MOTION

An oscillation in which the acceleration of an object is directly proportional to its displacement, and is directed towards the midpoint.

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PRESSURE

Force per unit area, measured in Pascal’s 1Pa=1N/m

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INTERNAL ENERGY

The sum of the random distribution of kinetic and potential energies associated with the molecules of a system

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SPECIFIC HEAT CAPACITY

The energy required to change the state of 1kg of a substance by 1K. Measured in J/Kg/K.

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ELECTRIC FIELD STRENGTH

Force per unit positive charge.

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MAGNETIC FLUX DENSITY

A measure of the strength of the magnetic field as given by B=F/ILsinθ measured in tesla (T).

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TESLA

Unit of magnetic flux density T. 1T is the magnetic flux density that will produce a force of 1N on 1m of wire carrying a current of 1A perpendicular to the direction of the magnetic field.

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MAGNETIC FLUX

The product of magnetic flux density and the area at right angles to the flux. Given by ∅=BAcosθ, measured in Weber (Wb).

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WEBER

Unit of magnetic flux Wb. 1 Wb is the flux when a magnetic flux density of 1T passes through an area of 1m squared at right angles

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MAGNETIC FLUX LINKAGE

The product of the magnetic flux and the number of turns on the coil it passes through. Given by Magnetic Flux Linkage=N∅, often measured in Weber turns.

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CAPACITANCE

The charge sored per unit potential difference, as given by C=Q/V , measured in farads (F).

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FARAD

Unit of capacitance F. 1 F is 1C of charge stored per volt.

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TIME CONSTANT (CR)

The time taken for the charge remaining on a capacitor to fall 1/e of its original value. It can be found using the expression CR, measured in seconds (s).

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PROTON/ATOMIC NUMBER

The number of protons inside a certain nucleus, also known as the atomic number.

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NUCLEON/MASS NUMBER

The number of neutrons added to the number of protons inside a certain nucleus, an alternative name for mass number.

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ISOTOPES

Nuclides with the same number of protons but different numbers of neutrons.

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ACTIVITY (A)

The number of radioactive decays per unit time, measured in Becquerel’s (Bq).

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DECAY CONSTANT (λ)

The probability of radioactive decay, given by λ=A/N, measured in (s^-1).

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HALF–LIFE

The average time taken for the activity of a radioactive source to decrease to one half of its original value.

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BINDING ENERGY

The energy required to separate an atom into its component parts.

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BINDING ENERGY PER NUCLEON

The average energy required to remove a nucleon from the nucleus.

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INTENSITY

Power per unit cross-sectional area. The energy incident per square metre of a surface per second measured in watts per metre squared (Wm^-2).

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ASTRONOMICAL UNITS (AU)

The average distance from the Earth to the Sun. 1AU=1.496 x 10^-11m

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PARSECS (pc)

A unit of distance originating from triangulation methods applied to space. 1Pc=3.086 x 10^16m

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LIGHTYEAR (ly)

The distance light travels in a year through a vacuum. 1ly=9.461 x 10^15m

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CRITICAL DENSITY (pc)

The average density of the universe above which the universe will collapse (closed universe) below and which the universe will expand forever (open universe). pc =9.5 x 10^-27 kgm^-3.

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PRINCIPLE OF CONSERVATION OF MOMENTUM

In the absence, of external forces, the total momentum of a system remains constant.

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NEWTON'S LAW OF GRAVITATION

The gravitational force of attraction between two bodies is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centres of mass.

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BOYLE'S LAW

The volume of a fixed mass of gas is inversely proportional to pressure exerted on it, provided temperature remains constant. pV=constant.

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AVOGADRO CONSTANT

One mole of any substance. 6.02x10^23 particles.

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SPECIFIC HEAT CAPACITY

The energy required to change the state of a 1kg of a substance by 1K. Energy change = mass x specific heat capactiy x change in temperature.

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FARADAY'S LAW

The magnitude of the induced e.m.f is equal to the rate of change of flux linkage.

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LENZ'S LAW

The induced e.m.f is always in such a direction as to oppose the change that caused it.

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## Other cards in this set

### Card 2

#### Front

Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object). F=Ma.

#### Back

NEWTON’S SECOND LAW

### Card 3

#### Front

When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction to that of the first body.

#### Back

### Card 4

#### Front

The product of mass and velocity. Momentum is always conserved

#### Back

### Card 5

#### Front

Net force on a body as equal to rate of change of its momentum

#### Back

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