# Physics Unit 4 Definitions

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- Created by: Lauren
- Created on: 02-05-14 17:31

Amplitude

The maximum displacement from equilibrium of an oscillating object

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Angular Displacement

The angle an object in circular motion turns through.

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Angular Speed

The rate of change of angular displacement of an object in circular (or orbital or spinning) motion.

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Angular Frequency

For an object oscillating at frequency f in simple harmonic motion, its angular frequency = 2(Pi)f

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Back EMF

EMF induced in the spinning coil of an electric motor or in any coil in which the current is changing. A back EMF acts against the applied pd.

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Capacitance

The charge stored per unit pd of a capacitor.

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Capacitor Energy

Energy stored by a the capacitor. Equations.

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Centripetal Force

The resultant force on an object that moves along a circular path. (Towards centre of the circle)

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Conservation of Momentum

For a system of interacting objects is the total momentum of the objects remains constant provided no external forces act on the system.

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Damped Oscillations

Oscillations that reduce in amplitude due to the presence of resistive forces such as friction and drag.

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Lightly Damped System

The amplitude of oscillations decreases gradually.

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Heavily Damped System

Displaced from equilibrium, then released, the system slowly returns to equilibrium without oscillating.

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Critically Damped System

The system returns to equilibrium in the least possible time without oscillating.

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Displacement

Distance in a given direction.

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Dissipative Forces

Forces that transfer energy which is wasted

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Eddy Currents

Unwanted induced currents in the metal parts of ac machines.

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Elastic Collision

An elastic collision is one in which the total kinetic energy after the collision is equal to the total kinetic energy before the collision.

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Electric Field Strength

At a point in an electric field, is the force per unit charge on a small positively charged object to move it from infinity to that point in the field.

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Electromagnetic Induction

The generation of an emf when the magnetic flux linkage through a coil changes or a conductor cuts across magnetic field lines.

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Equilibrium

State of an object when at rest or in uniform circular motion.

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Equipotential

A line or surface in a field along which the electric or gravitational potential is constant.

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Explosion

When two objects fly apart, the two objects carry away equal and opposite momentum.

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Faraday's Law of Electromagnetic Induction

The induced emf in a circuit is equal to the rate of change of magnetic flux linkage through the circuit.

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Fleming's Left Hand Rule

Rule that relates the directions of the force, magnetic field and current on a current-carrying conductor in a magnetic field.

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Fleming's Right Hand Rule

Rule that relates the directions of the induced current, magnetic field and velocity of the conductor when the conductor cuts across magnetic field lines and an emf is induced in it.

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Force

Rate of change of momentum.

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Free Oscillations

Oscillations where there is no damping and no periodic force acting on the system so the amplitude of the oscillations is constant.

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Forced Oscillations

Oscillations of a system that is subjected to an external periodic force.

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Frequency

Of an oscillating object is the number of cycles of oscillations per second.

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Geostationary Satellite

A satellite that stays above the same point on the Earth's equator as it orbits the Earth because its orbit is in the same plane as the equator, its period is exactly 24h and it orbits in the same direction as the Earth's direction of rotation.

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Gravitational Constant G

The constant of proportionality in Newton's Law of Gravitation.

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Gravitational Field

The region surrounding an object in which it exerts a gravitational force on any other object.

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Gravitational Field Strength g

The force per unit mass on a small mass placed in the field.

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Gravitational Force

An attractive force that acts equally on any two objects due to their masses.

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Gravitational Potential V

At a point in a gravitational field is the work done per unit mass to move a small object from infinity to that point.

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Gravitational Potential Energy

At a point in a gravitational field is the work done to move a small object from infinity to that point.

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Grid System

The network of transformers and cables that is used to distribute electrical power from power stations to users.

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Hall Probe

A device used to measure magnetic flux density.

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Impulse

A force acting on an object, force x time for which the force acts.

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Line of Force or Field Line

A line followed by a small mass in a gravitational field or a small positively charged object in an electric field or a free north pole in a magnetic field acted on by no other forces than the force due to the field.

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Magnetic Flux

=BA for a uniform magnetic field of flux density B that is perpendicular to the area A

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Magnetic Flux Density B

The magnetic force per unit length per unit current on a current carrying conductor at right angles to the field lines.

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Magnetic Flux Linkage

Through a coil of N turns = NBA

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Momentum

Mass x Velocity

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Motor Effect

The force on a current carrying conductor due to a magnetic field.

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Natural Frequency

The frequency of free oscillations of an oscillating system.

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Periodic Force

A force that varies regularly in magnitude with a definite time period.

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Permittivity of Free Space

The charge per unit area in coulombs per square metre on oppositely charged parallel plates in a vacuum when the electric field strength between the plates is 1 volt per metre.

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Potential Gradient

At a point in a field is the change of potential per unit change of distance along the field line at that point. Potential gradient=field strength at any point.

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Principle of Conservation of Momentum

When tow or more bodies interact, the total momentum is unchanged, provided no external forces act on the bodies.

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Principle of Conservation of Energy

In any change the total amount of energy after the change is always equal to the total amount of energy before the change.

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Radial Field

A field in which the field lines are straight and converge or diverge as it from a single point.

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Resonance

The amplitude of vibration of an oscillating system subjected to a periodic force is largest when the periodic force has the same frequency as the resonant frequency of the system.

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Resonant Frequency

The frequency of an oscillating system in resonance.

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Satellite

A small object in orbit around a larger object.

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Simple Electric Motor

An electric motor with an armature consisting of a single coil of insulated wire.

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Simple Harmonic Motion

Motion of an object if its acceleration is proportional to the displacement of the object from equilibrium and is always directed towards the equilibrium position.

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Time Constant

The time taken for a quantity that decreases exponentially to decrease to 0.37 of its initial value. For a capacitor, resistance x capacitance.

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Time Period

Time taken for one complete cycle of oscillations.

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Transformer

Converts the amplitude of an alternating pd to a different value. Consists of 2 insulated coils, the primary coil and the secondary coil, wound around a soft iron core.

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Transformer Rule

The ratio of the secondary voltage to the primary voltage is equal to the ratio of the number of secondary turns to the number of primary turns.

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Uniform Circular Motion

Motion of an object moving at constant speed along a circular path.

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Uniform Field

A region where the field strength is the same in magnitude and direction at every point in the field.

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Work Done

Work is energy transferred by means of a force.

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## Other cards in this set

### Card 2

#### Front

The angle an object in circular motion turns through.

#### Back

Angular Displacement

### Card 3

#### Front

The rate of change of angular displacement of an object in circular (or orbital or spinning) motion.

#### Back

### Card 4

#### Front

For an object oscillating at frequency f in simple harmonic motion, its angular frequency = 2(Pi)f

#### Back

### Card 5

#### Front

EMF induced in the spinning coil of an electric motor or in any coil in which the current is changing. A back EMF acts against the applied pd.

#### Back

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