# Physics G485 State and Define Points

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Define electric field strength.
Force per unit positive charge, given by E=F/q.
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Define Coulomb's law.
The force between two charges is proportional to the product of the charges and inversely proportional to the square of the distance between the charges.
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Define magnetic flux density.
A measure of the strength of the magnetic field. Measured in Tesla.
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Define a tesla.
Unit of magnetic flux density.
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Define magnetic flux.
The product of magnetic flux density and the area at right angles to the flux. Measured in weber (Wb).
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The magnitude of the induced e.m.f. is equal to the rate of change of flux linkage.
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State Lenz's law.
The direction of any induced current is in a direction that opposes the flux change that causes it.
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Define capacitance.
The charge stored per unit potential difference, as given by C = Q/V. Measured in farads (F).
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Unit of capacitance (F). 1F is 1C of charge stored per volt.
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Define the time constant of a circuit.
The time taken for the charge remaining on a capacitor to fall to 1/e of its original value. Measured in seconds.
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Define Proton number.
The number of protons inside a certain nucleus. Also known as the atomic number.
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Define Nucleon number.
The number of neutrons added to the number of protons inside a certain nucleus.
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Define Isotopes.
Nuclides with the same number of protons but different number of neutrons.
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Define activity.
The number of radioactive decays per unit time. Measured in becquerels (Bq).
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Define decay constant.
The probability of radioactive decay, measured per second.
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Define 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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Define binding energy.
The energy required to separate an atom into its component parts.
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Define light years.
The distance light travels in a year through a vacuum. 9.5 x 10^15 m.
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Define parsecs.
A unit of distance originating from triangulation methods applied to Space. 3.1 x 10^16 m.
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Define an astronomical unit.
The average distance from Earth to the Sun. 1.5 x 10^11 m.
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A paradox dealing with the finite or infinite nature of the universe. With an infinite numbers of stars in an infinite universe, no matter what direction you look you will always see a star along your line of sight. Therefore night would be bright.
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State Hubble's law.
The speed of recession of a galaxy is directly proportional to its distance from the Earth.
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State the cosmological principle.
On a large scale the universe is uniform.
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Define critical density.
The average density of the universe above which the universe will collapse (closed universe) and below which the universe will expand forever (open universe).
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## Other cards in this set

### Card 2

#### Front

Define Coulomb's law.

#### Back

The force between two charges is proportional to the product of the charges and inversely proportional to the square of the distance between the charges.

### Card 3

#### Front

Define magnetic flux density.

Define a tesla.

### Card 5

#### Front

Define magnetic flux.