# OCR A2 Physics Definitions

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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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The magnetic flux through the coil multiplied by the number of turns on the coil. Measured in weber turns
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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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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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## Other cards in this set

### Card 2

Explain equation

#### Back

Magnetic flux density

### Card 3

#### Front

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

#### Back ### Card 4

#### Front

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.

#### Back ### Card 5

#### Front

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.

#### Back 