Electricity
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- Created by: Jen56
- Created on: 01-01-18 21:02
What is potential difference?
The energy transferred per coulomb of charge
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Why is a voltmeter placed in parallel?
We are comparing an energy change per coulomb before and after the component
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What is one volt?
One joule of energy transferred per coulomb
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What is potential difference equal to?
V=E/Q = W/Q
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What is electrical current?
The rate of flow of charge
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What carries charge in electrical circuits?
Free electrons within the conductors making up the circuit
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In which direction does conventional current flow?
From the positive terminal to the negative
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What is current equal to?
I=Q/t
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What is Kirchoff's rule for voltage?
The sum of the p.d.s around any circuit loop is 0.
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What is Kirchoff's rule for current?
The current flowing into any point is the same as the current flowing out of that point.
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What is resistance?
The opposition of the flow of current through a material or component
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What is resistance equal to?
R=V/I
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What is an ohmic resistor?
A material which has a constant resistance. It follows ohms law (v=ki)
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What does Ohm's law only apply to?
Constant conditions e.g. temperature
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Does a diode follow ohm's law?
No
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Draw and explain the diagram for the resistance of a diode.
When p.d is -ve, there is no current and no resistance as the diode blocks electrical current in one direction. High resistance when current is +ve
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Does a filament bulb follow ohm's law? Why?
No. Bulb heats up when current passes through it which produces light as a result. R increases as temperature increases but this levels off at high and low p.d.s. R increases because metal ions in the wire vibrate more, increasing collisions and R.
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Describe the charge carriers in a conductor. Resistance?
Many charge carriers and free to move. In metals, these are delocalised electrons. Low resistance increasing with temperature.
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Describe the charge carriers in an insulator. Resistance?
Little/no free charge carriers. They are all taken up in bonding. High resistance.
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Describe the charge carriers in semiconductors. Resistance?
The charge carriers need an "incentive" in terms of energy so that they become free to move. Variable resistanve - the more energy given to the semiconductor, the lower the resistance.
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Describe the resistance of a superconductor? Current?
Loses all resistance below the critical temperature (different for different materials). Current set in a loop of superconducting material flows indefinetly.
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What do superconducting materials do with magnetic fields? Uses due to this?
Superconductors exclude magnetic fields inside them. Magnetic levitation, strong magnets.
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As length increases, resistance...
Increases
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As cross-sectional area increases, resistance...
Decreases
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What are the rules for resistor combinations in series and parallel circuits?
R=R1+R2. 1/Rtot = 1/R1 + 1/R2
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What do we assume when performing circuit calculations?
Ammeters have 0 R. Voltmeters have infinite R. Wires have 0 R. Cells have 0 R.
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What do cells/ batteries etc. have in reality?
An internal resistance
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What is electromotive force?
The maximum energy transferred to each coulomb of charge. The total power generated by the cell.
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What is the terminal p.d?
The actual energy per coulomb delivered to the circuit.The power delivered to the circuit.
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What is the load resistance?
The total effective resistance of the circuit connected to the cell.
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What is the internal resistance?
The resistance due to the inherrent properties of the cell material.
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What does I represent?
The current that flows in the circuit due to the emf and the load and internal resistors.
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What is the 'lost power'?
The power dissipated inside the cell.
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What is the total emf of cells in series?
The emfs add up, as long as the cells are connected correctly.
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What is the total emf of cells in parallel? Why?
Total emf is that of one cell. This is because "a coulomb" cannot pass through both cells.
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What are potential dividers?
Simple circuits which are used to control the potential differnce in the circuit (change a fixed pd into a variable pd).
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What does a potential divider circuit normally consist of?
A fixed p.d. power supply, a fixed resistor, a variable resistor.
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Other cards in this set
Card 2
Front
Why is a voltmeter placed in parallel?
Back
We are comparing an energy change per coulomb before and after the component
Card 3
Front
What is one volt?
Back
Card 4
Front
What is potential difference equal to?
Back
Card 5
Front
What is electrical current?
Back
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