Flashcards in Electricity Deck (84)
Which way do electrons flow in a circuit?
From the - to the + terminal.
The rate of flow of charge.
Which way does charges flow in a circuit?
From the + to the - terminal.
Define a coulomb.
The amount of charge that passes 1 second when the current is 1 ampere.
How is current calculated?
Change in charge
Change in time.
The energy converted per unit charge moved.
How is voltage calculated ?
Work divided by charge.
Define a volt.
The potential difference across a circuit is 1 volt when 1 joule of energy is converted moving 1 coulomb of charge through the component.
What happens when PD is put through an electrical component?
A current will flow.
How is resistance calculated?
Voltage divided by current.
What is a resistance of 1 ohm?
A component has a resistance of 1 when a PD of 1v makes a current of 1A flow through it.
What is Ohm's law?
Provided the temperature is constant, the current through an ohmic conductor is directly proportional to the potential difference across it.
What is an ohmic conductor ?
A component with constant resistance.
The voltage is directly proportional to the current.
What does the gradient of an I/V graph show?
The resistance of an electrical component. The flatter the gradient, the greater the resistance.
What is the circuit you might use to calculate the resistance of a component?
Have a battery connected to a variable resistor. Connect this to the component, this to an ammeter and this to the battery. A voltmeter should be in parallel to the component.
What is the I/V graph of a filament lamp?
It is a curve. At the origin it is steep but as voltage increases in both directions, it gets flatter.
Explain the shape of the I/V graph of the filament lamp.
The filament lamp is a coiled up piece of wire. Thus current flowing though it causes the temperature to increase and the resistance increases.
How does a semiconductor work?
They have less charge carriers available in them so they aren't as good at conducting as metal. If energy is supplied, then there are more charge carriers so the resistance drops.
Name 3 types of semiconductors
Thermistor, LDR and diode.
How do diodes work?
They let current flow in one direction only as they have a very high resistance in one direction.
What do most diodes have a threshold voltage of ?
0.6 v. They need this before they can conduct.
What 3 things can affect the resistance of a piece of wire?
Length(longer it is, the more stuff the electrons have to get past)
Area(the wider, the more ways the electrons can get past)
Resistivity.(this depends on the material. It can be changed by the structure or by environmental factors like temperature and light intensity.
What is the definition of restistivity?
State the equation from the formula sheet and state which each letter represents.
What is the unit for restistivity ?
Ohm-meters. Don't write Ω/m. Write Ωm
What is the formula for restistivity ?
P = RA
How big are the typical restistivity values for conductors?
Very small. For copper is is 0.00000000172
What is the disadvantage if resistance in a circuit?
Energy gets waste as heat.
How can the restistivity of a material be reduced?
Cool it down.
What is the transition temperature?
If a material is cooled to below this point, then restistivity goes away.