AS Electricity Flashcards
(31 cards)
What is electric current (with units)
The rate of flow of charge. Measured in Amps(A)
What is potential difference
The work done moving a unit charge between 2 points in a circuit
V=W/Q
What is resistance
How difficult it is for current to flow through an appliance
A component has resistance of 1 ohm if 1A flows through it when a P.D of 1V is applied across it
R=V/I
What is meant by an ohmic conductor
A conductor that obeys ohms laws
What is P.D and current like in an ohmic conductor
Current is directly proportional to P.D providing physical conditions remain constant
How do you measure current in a circuit
Ammeter connected in series with the component
How do you measure the potential difference across a component
Connect a voltmeter in parallel across the component
What does the gradient of a current-P.D graph represent
Rate of charge with respect to voltage
Explain the graph of a filament lamp
As the current increases, the resistance also increases. A big increase in the voltage produces only a small increase in the current
Why dies the current increasing on the filament lamp cause an increase in the resistance
As current flows through the lamp, electrical energy is converted to heat energy so the metal ions vibrate with increased amplitude. This impedes the movement of electrons through the lamp as they collide with the ions
What is a diode
A diode is an appliance that only allows current to flow in one direction
Should you assume that voltmeters rot have zero resistance or infinite resistance
Infinite resistance
What does the graph of a semiconductor diode represent
The forward bias is the direction in which it will allow current to flow easily past the threshold voltage, which is the smallest voltage needed to flow. In the direction of the reverse bias, the resistance of the diode us extremely high meaning that only a very small current can flow
Why should you assume that an ammeter has zero resistance unless stated otherwise
There would be 0 potential difference across their ammeter and no energy is lost across it, it doesn’t effect the circuit
What is an LDR
A semi conductor that is sensitive to light , as the light intensity increases, the resistance decreases
How does a thermistor work
As the temperature increases, the resistance decreases. They have a negative temperature coefficient
What is resistivity
The resistance if a 1m cylinder with a cross sectional area of 1m^2. It’s a property of a material
P = RA/L
What is a superconductor
A material that has a resistivity of zero at or below a critical temperature. The critical temperature is an inherent property of the material.
How do you find the total resistance in a series circuit
Rt = R1 + R2 + R3
If 6 cells each of voltage 5v are arranged in parallel what is the voltage of the circuit
5V
If 6 cells each are 5V are placed in series what is the overall voltage
30V
How does the current vary between each component of a series circuit
The current through all components is the same so the current does not vary
Is the current in parallel components the same
No each branch can have different currents - Kirchhoffs first law
What is Kirchoffs first law
All of the current going into a junction is equal to the current leaving the junction
