Electricity Flashcards
Define current
Net flow of charged particles per unit time
Define potential difference
- Energy transferred per unit charge when electrical energy is converted into another form of energy
- 1V = 1 J/C
Define resistance
A materials opposition to the flow of electric current
Define Ohm’s Law
For a given material, voltage is directly proportional to current at a constant temperature
What are I-V characteristics?
Graph showing how current flowing through a component changes with increasing voltage
Describe the I-V characteristics graph for an ohmic conductor
Straight constant gradient
Describe the I-V characteristics graph for a filament lamp
- Bottom left is increasing curved gradient
- Top right has decreasing curved gradient
Describe the I-V characteristics graph for a diode
- Far end of negative p.d has very low negative current
- Current doesn’t go above 0 until V > 0.6
- After 0.6V, gradient curves upward steeply
Define resistivity
A property of a material that determines the resistance of a piece of given dimensions
What is units for resistivity?
Ωm / ohm metres
What are semiconductors?
- A group of materials which conduct electricity, but not as good as metals
- When temperature rises, they can release more carriers and their resistance decreases
State 3 common semiconductor components
- Thermistors
- Diodes
- Light dependent resistors(LDR)
What is a thermistor?
- A component with a resistance that changes with temperature
- Resistance decreases as temperature increases
- Temperature is normally controlled using a water bath
What is a LDR?
- A component with a resistance that changes with light intensity
- Resistance decreases as light intensity increases
What is a superconductor?
A material that has zero resistivity and zero resistance when cooled below a critical temperature
State 3 uses of superconductors
- Power cables that transmit electricity without power loss
- Really strong electromagnets with applications such as Maglev trains
- Electronic circuits that work really fast with minimal energy loss due to having no resistance to slow current down
Define power
Energy transferred per second in Watts
What is the equation for Energy involving power?
E = Pt
Define internal resistance
The resistance of the materials within the battery
How does internal resistance occur?
Electrons in the chemical reactions collide with the atoms in the battery, losing energy which causes resistance
Define electromotive force, emf
- Energy transferred from chemical to electrical energy in a power system
- Electrical energy per unit charge, in volts
Define terminal p.d
- Energy transferred from electrical energy to another type
- Work done per unit charge, in volts
For a V-I graph, what does the y-intercept represent?
emf
For a V-I graph, what does the gradient represent?
Negative internal resistance
State Kirchoff’s first law and the principle it’s based on
- Sum of the currents entering a circuit = Sum of the currents leaving the circuit
- Conservation of charge
State Kirchoff’s second law and the principle it’s based on
- Sum of the EMFs around a circuit loop = Sum of the PDs around that loop
- Conservation of energy
What is constant in a series circuit?
Current
What is constant in a parallel circuit?
Voltage
How do you find the total emf of cells in a series circuit?
ϵ(total) = ϵ1 + ϵ2 + ϵ3
How do you find the total emf of cells in a parallel circuit?
- ϵ(total) = ϵ1 = ϵ2
- When cells are identical
What is a potential divider?
- A circuit containing a voltage source and a pair of resistors
- The voltage across one resistor is used as an output voltage
- If resistors aren’t fixed, the circuit will be capable of producing a variable output voltage
State the relationship between resistance and length
Resistance is proportional to length
State the relationship between resistance and cross-sectional area
Resistance is inversely proportional to cross-sectional area
State the relationship between temperature and resistance for a metal conductor
As temperature increases, resistance increases
Describe the relationship between temperature and resistance for a metal conductor
- Resistance increases as temperature increases
- As fixed ions of the metal gain energy and vibrate
- This causes charge carriers to collide more, making them slow down
- Therefore current decreases, which increases resistance
State the equation for the output voltage of a potential divider?
V(out) = R(2) x V(in)/ R(1) + R(2)
