# Unit 1 Definitions

Electromotive Force (Emf)
The amount of electrical energy produced by a battery/source per unit charge, measured in volts.
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Power
Rate of transfer of electrical energy to a component per second, measured in watts.
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Resistance
Potential difference divided by current, it is the electrical energy used when a current of 1 amp moves through a component, measured in ohms.
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Electrical Current
Number of charged particles passing a point per second, measured in amps.
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Potential Difference/Voltage
The amount of electrical energy converted or transferred per unit charge between two points, measured in volts.
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Ohm's Law
The current passing through a conductor is proportional to the voltage, as long as the physical conditions remain the same (temperature etc.).
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Resistivity
The resistance of a 1m^2 cross section conductor with length 1m.
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Critical Temperature
The temperature that below which a superconductor has no resistance and very large currents can pass through with very small voltage/very small energy losses.
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Internal Resistance
An electrical source or cell's opposition the flow of charge through it, defined as the loss of pd per unit current when a current passes through the source/cell.
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Isotopes
Nuclides with the same number of protons but different number of neutrons in their nuclei.
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Pair Production
When a particle and its corresponding anti-particle are produced from a photon with energy greater than the total rest energy of the two particles.
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Annihilation
When a particle and its corresponding anti-particle collide they annihilate, converting their kinetic energy and rest energies into two high energy photons (with energy E=hf).
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## Other cards in this set

### Card 2

#### Front

Rate of transfer of electrical energy to a component per second, measured in watts.

Power

### Card 3

#### Front

Potential difference divided by current, it is the electrical energy used when a current of 1 amp moves through a component, measured in ohms.

### Card 4

#### Front

Number of charged particles passing a point per second, measured in amps.

### Card 5

#### Front

The amount of electrical energy converted or transferred per unit charge between two points, measured in volts.