Electric Circuits
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- Created by: dkoning00
- Created on: 30-04-17 18:58
What is charge?
A property particles have - it may be positive, negative or neutral
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What is the charge of an electron?
-1.6x10^-19 Coulombs
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What is current?
The rate of flow of positive charge
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How do you calculate current?
Charge passing a point divided by time taken
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What is potential difference?
The work done per coulomb of charge passing a point
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How do you calculate potential difference?
Work done divided by charge passing a point
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What is EMF?
Electromotive force is the energy transferred to each coulomb of charge at a source
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Describe how PD is different to EMF
PD is the energy transferred from the charge, EMF is the energy transferred to the charge
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What is resistance? Give the formula
Resistance is the ratio of potential difference across to current through a component. R=V/I
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How do you calculate work done by a circuit?
W = VIt
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What is resistivity? Give the formula
A value for comparing electrical resistance of materials. Resistivity = (resistance × cross-sectional area) ÷ length
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State Ohm's Law
For metals at a constant temperature, the current in the metal is proportional to the potential difference across it
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What happens to current in series?
On a single branch (or loop) of a circuit, the current is the same all the way around - current isn't used up
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What happens to current in parallel?
At a junction (or branching) of a circuit, the current is shared inversely proportional to the resistance of each branch
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What happens to p.d. in series?
Components connected in series along a branch (or loop) will share the supplied potential difference in proportion to their resistances (i.e. more p.d. across components with higher R)
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What happens to p.d. in parallel?
In parallel, each branch (or loop) has the same potential difference supplied across it
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How do you calculate total series resistance?
Total resistance = R1 + R2 + R3 + ...
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How do you calculate total parallel resistance?
1/Rtotal = 1/R1 + 1/R2 + …
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What is drift velocity?
Speed at which a charge carrier moves through a conductor when a current flows
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Give a typical value for drift velocity
0.1 mm s^-1 ish
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What is the charge carrier density?
The number of charge carriers (i.e. free electrons) per unit volume
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What equation links drift velocity and charge carrier density and what does each symbol represent?
I = nqvA Current = charge carrier density x charge of an electron x drift velocity x cross-sectional area
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What is a conductor?
Material with a large amount of free electrons and low resistance
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What happens when a conductor is heated?
the lattice of atoms in the material vibrates more, causing an increase in resistance. This causes a decrease in current
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What is a semi-conductor?
Material with fewer free electrons than a conductor and therefore higher resistance
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What happens when a thermister is heated?
The atoms in the material release more electrons, causing a decrease in resistance. This causes an increase in current.
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What happens when light is shone on an LDR?
Light decreases the resistance by releasing more electrons
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What is an insulator?
Material with a very low number of free electrons, so have high resistances
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What happens when an insulator is heated?
When temperature increases in an insulator, the lattice of atoms in the material vibrates more, causing an increase in resistance. This causes a decrease in current
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What is internal resistance?
The resistance inherent to an emf source or power supply. Causes a dissipation of energy inside the source, and so there is some p.d. wasted or ‘lost’
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What are 'lost volts'?
The p.d. dissipated (as heat) inside a source or power supply due to its internal resistance, r. As ‘lost volts’ = Ir, the larger the current, the more p.d. is dissipated within the power source
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What is the terminal potential difference?
The p.d. available to a circuit, once some has been lost due to the internal resistance of the source. This is the p.d. that is measured across the terminals of a power source
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State the principle of conservation of electrical energy
The sum of the emf’s is equal to the sum of the pd’s
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What does the sum of the terminal p.d. and lost volts equal?
EMF (ε)
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What is a potential divider?
A circuit that consists of two (or more) resistors in series that share a potential difference between them
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What is a potentiometer?
A component that divides potential into two (like two resistors R1 & R2) with a fixed total resistance
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Why is current through a potentiometer always the same?
Because it is in series
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How do you measure EMF and internal resistance of a power source?
By plotting V against I with differing resistance values and a line of best fit, EMF is equal to the y-intercept and r is equal to the negative of the gradient
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Other cards in this set
Card 2
Front
What is the charge of an electron?
Back
-1.6x10^-19 Coulombs
Card 3
Front
What is current?
Back
Card 4
Front
How do you calculate current?
Back
Card 5
Front
What is potential difference?
Back
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