# OCR A2 Physics Definitions

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- Created by: Lucyl57
- Created on: 07-06-13 16:16

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- Created by: Lucyl57
- Created on: 07-06-13 16:16

Electric field strength

The force per unit positive charge

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Magnetic flux density

Explain equation

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Tesla

One tesla is the magnetic field strength when a wire of length one metre and carrying a current of one ampere at a right angle to the field experiences a force of one newton

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Magnetic flux

The magnetic flux through an area A is defined as the product of the magnetic flux density B and the projection of area A onto a surface at right angles to the flux.

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Weber

One weber is the magnetic flux when a magnetic field of magnetic flux density of one tesla passes at right angels through an area of one square metre.

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Magnetic flux linkage

The magnetic flux through the coil multiplied by the number of turns on the coil. Measured in weber turns

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Faraday's law of electromagnetic induction

the magnitude of the induced emf is equal to the rate at which magnetic flux is cut.

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Lenz's law of electromagnetic induction

the direction of any induced current is in a direction that opposes the flux change that causes it.

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Capacitance

the charge stored per unit potential difference. Its unit is the farad (F).

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Farad

One farad is one coulomb per volt.

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The time constant of a circuit

time constant = capacitance multiplied by resistance.

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Nucleon number A

The number of nucleons in any nucleus.

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Proton number Z

The number of protons in the nucleus

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Isotope

Two nuclides with the same number of protons but different numbers of neutrons

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Activity (A)

The rate at which a source emits radioactive particles

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Becquerel

One Becquerel equals an activity of one particle emitted per second.

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The decay constant

Activity of the source divided by the number of nuclei present.

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Half-life

The time taken for the activity of the source to decrease by one half. It is also the time taken for the number of radioactive nuclei to decrease by one half.

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Binding energy

The energy required to separate an atom into its constituent 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

The power per unit cross-sectional area.

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Acoustic impedance (Z)

Used to determine the fraction of the intensity refracted at a boundary between two materials of different acoustic impedances. Defined by Z=pc where p is the density of the material and c is the speed of sound in the material.

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1 AU

1.496 times 10 to the 11

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1 Pc

3.086 times 10 to the 16

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1 ly

9.461 times 10 to the 15

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Hubble's law

The speed of the recession of a galaxy is directly proportional to its distance from the Earth.

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Cosmological principle

States that on a large scale the universe is uniform. The universe is isotropic (the same in all directions) and homogeneous (of uniform density)- as long as a large enough volume is used.

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Critical density

The average density of the universe above which the universe will collapse and below which the universe will expand forever.

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Explain equation

Magnetic flux density

One tesla is the magnetic field strength when a wire of length one metre and carrying a current of one ampere at a right angle to the field experiences a force of one newton

The magnetic flux through an area A is defined as the product of the magnetic flux density B and the projection of area A onto a surface at right angles to the flux.

One weber is the magnetic flux when a magnetic field of magnetic flux density of one tesla passes at right angels through an area of one square metre.

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