AS Physics- Electricity

Question	Answer
How are current and charge related?	1 coulomb of charge is the quantity which passes any point in the circuit in which a 1A current flows for 1 second.
Define the coulomb	A coulomb is the amount of charge that passes in one second when the current is 1A.
Define potential difference	The potential difference across a component is 1 volt when you convert one joule of energy moving 1 coulomb of charge through a component.
Name an environmental factor likely to alter the resistance of a component?	Temperature
What is special about an ohmic conductor?	Resistance is always constant (on the IV graph, the gradient is constant).
What does the circuit used to determine the IV characteristics of a component look like?	A switch, variable resistor, ammeter and component in series with a voltmeter across the component in parallel.
For a filament lamp, what is the relationship between the resistance and temperature of a metal? What does this look like on a graph?	As the resistance increases, the temperature increases. On a graph, there will be a curve passing through the origin. At the origin, it starts steep and gets shallower as the voltage rises.
Why does the graph of a diode look like it does?	Because they only allow current to flow in one direction and require a threshold voltage 0.6V before they'll conduct. In reverse bias, the resistance is very high and the current that flows is very small.
What is an LDR?	The greater the intensity of light shining on an LDR, the lower it's resistance. light provides more energy that releases more electrons therefore there is a higher charge and a lower resistance.
What happens to a superconductor when it's cooled to it's critical temperature?	It no longer has any resistance, and therefore no electrical energy is converted to heat so no energy is wasted.
Give some uses of superconductors	1) Power cables that transmit electricity without any loss of power. 2) Strong electromagnets that don't need a constant power source. 3) Electronic circuits that work really fast as there's no resistance slowing them down.
What are the units for resistivity?	Ohm metres
What is the equation linking power, current and resistance?	V = I^2 R
What equation links power, voltage and resistance?	P = V^2 / R
What causes internal resistance?	The resistance within a battery, or other voltage source, that causes a drop in the source voltage when there is a current. The more resistance a battery has, the higher its internal resistance.
What is the difference between e.m.f and terminal p.d?	The electromotive force (emf) is the potential difference of a source when no current is flowing. Terminal voltage is the voltage output of a device is measured across its terminals.
Kirchhoff's first law states that the total current entering a junction...	Equals the totals current leaving it
Kirchhoff's second law states that the total e.m.f around a series circuit...	Equals the sum of the p.d's across each component.
What is a potential divider?	A circuit with a voltage source and a few resistors in series. The potential of the power supply is divided in the ratio's of the resistors. Therefore, you can choose the resistances to get the voltage you want across them.
Define the term "time period" for an alternating signal	The time period the the time it takes to complete on cycle. Found by measuring the distance between successive peaks.
How do you find the frequency?	1 / time period
Why are rms values used?	In order to compare AC and DC voltages, you need to take an average, however this is impossible with AC since the average would be zero due to the shape of the graph (they'd cancel). You can use the rms, and for a sine wave, you divide the peak voltage (or current) by root 2.

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AS Physics- Electricity

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	Created by Lauren Robinson over 9 years ago