# Physics G485 definitions

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- Created by: Emily B
- Created on: 19-02-13 22:43

Electric Field Strength

Force per unit positive charge

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Magnetic Flux Density

The strength of the magnetic field

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Tesla

The SI unit for magnetic flux density. 1T = 1NA^-1m^-1

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Magnetic Flux

The product of magnetic flux density normal to a circuit and the cross-sectional area of the circuit. unit is Weber's

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Magnetic Flux Linkage

The product of the magnetic flux and the number of terms

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Faraday's Law

The emf induced is equal to the rate of change of magnetic flux linkage or the rate of flux cutting

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Lenz's Law

The induced current or EMF is in a direction so as to produce effects which oppose the change producing it

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Capacitance

The ratio of change stored by a capacitor to the PD across it

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Farad

Unit of capacitance. 1F = 1CV^-1

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Time Constant of a circuit

The time taken for the current, charge stored or PD to fall to 1/e (about 37%) when a capacitor discharges through a resistor. It is also equal to the product of capacitance and resistance

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Coulomb's Law

Any two point charges exert an electrical force on each other that is proportional to the product of their charges and inversely proportional to the square of the distance between them

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Newton's Law of Gravitation

Any two point masses attract each other with a force that is proportional to the sum of their masses and inversely proportional the square of their seperation

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Nucleon number

The number of protons and neutrons in the nucleus of an atom

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Isotopes

Nuclei of the same element with a different number of of neutrons but the same number of protons

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Activity

The rate of decay or disintegration of nuclei in a radioactive sample

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Decay Constant

The constant for an isotope that appears in the equation A = lambda*N. It is equal to the probability of an isotope decaying per unit time interval

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Half-Life

The mean time taken for half the number of active nuclei in a radioactive sample to decay

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Binding Energy

The minimum external energy required to seperate all the neutrons and protons of a nucleus

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Intensity

Power per unit cross-sectional area

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Olber's Paradox

For an infinite, uniform and static universe, the night sky should be bright because of light received in all direction from stars

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Hubble's Constant

The ratio of the speed of a receding galaxy to its distance from the observer. =v/x

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Cosmological Principle

A principle that states that the universe has the same large-scale structure when observed from any point in the universe

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Critical Density

The density of the university that will give rise to a flat universe.

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Black Hole

The remnant of a massive star formed as a result of matter collapsing to a singular point. The density of a black hole is so intense that even light cannot escape from it.

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Braking radiation

X-rays produced when electrons are decelerated

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Chandrasekhar limit

The maximum mass of a white dwarf - about 1.4 solar masses

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Closed universe

A model of the universe in which gravitational force is strong enough to halt its expansion and reverse the process towards a Big Crunch

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Dark matter

Matter that emits or reflects little EM radiation making it very difficult to detect

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Electron Degeneracy Pressure

Pressure created by closely packed electrons in a white dwarf due to Pauli's exclusion principle

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Larmor Frequency

The frequency of precession of nuclei in an external magnetic field

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Light year

The distance travelled by light in one year. =9.5x10^15 m

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Metastable

Describes a nucleus that is unstable but relatively long-lived state

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Open Universe

A model of the universe in which gravitational force cannot halt the expansion of matter.

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Redshift

The shifting of the entire spectrum of a receding source to longer wavelengths

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## Other cards in this set

### Card 2

#### Front

The strength of the magnetic field

#### Back

Magnetic Flux Density

### Card 3

#### Front

The SI unit for magnetic flux density. 1T = 1NA^-1m^-1

#### Back

### Card 4

#### Front

The product of magnetic flux density normal to a circuit and the cross-sectional area of the circuit. unit is Weber's

#### Back

### Card 5

#### Front

The product of the magnetic flux and the number of terms

#### Back

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