Yr 12 - Charge & Current - 1 Flashcards
Electric Potential Energy
Energy required to move a charge against an electric field.
Potential Energy OR (Potential)
Potential energy per unit charge.
Potential = JC^-1
- So we don’t have to worry about how much charge there is.
Potential VS Electrical potential energy
- Potential depends on ‘Separation Distance’
- Electrical Potential Energy depends on ‘Separation Distance’ & ‘Charge Size’.
Charge
Physical property that causes matter to move.
- Coulomb’s
How to the 3 charges interact with each other?
Positive - Negative = Attract
Positive - Positive = Repel
Neutral = No interaction
Potential Difference
Difference in electric potential energy between 2 points.
- Due to charge doing work on circuit components.
Why are Thunderstorms so powerful?
✱ (-) charge builds any bottom of storm cloud
✱ Earths surface is made of (+) & (-) charge
✱ (-) cloud charge attracts (+) ground and repels (-) ground.
✱ Therefore, net (+) ground and net (-) cloud.
✱ Higher cloud = Greater separation distance. ∴ greater Ep
✱ Each (-) lightning charge looses up to 1,000,000J as its hits the ground (Potential Difference)
✱ Ep converted into Ke ∴ very hot
EMF
Electric Potential produced by a source of EMF (battery, power supply etc)
- EMF source does work on charges passing through
- Term used for components that increase Ep of charge.
Electric Current
Rate of flow of charged particles (Amps)
1 Amp
1 coulomb passing a point per second
Usual Direction of current flow
(+) to (-)
Conventional Current
Current flowing from (+) to (-).
Electron Flow
Flow of electrons from (-) to (+) as negatively charged.
- Opposite to conventional current
Equation for Charge
Q = I T
- Ignore (-) and just use modulus. (Check with Teacher)
Charge of an electron and Proton
e = -1.6 x 10 ^-19
p = 1.6 x 10 ^-19
Equation for number of electrons
No e = Total charge / e (electron charge).
Kirchhoff’s 1st Law
Sum of current into a node/junction = sum of current out.
- Due to conservation of charge
Conservation of charge
Charge cannot be created/destroyed. The sum of charge in any interaction must be the same before and after.
1 Coulomb
Charge flowing through a point per second where there is 1A current.
Formula for No electrons (No e)
NO e = ∑ Current / e
e = Charge of electron (-1.6x10^-19)
Conductor
Material with a high charge carrier density.
- Current free to flow
Semi-Conductor
Material with a medium charge carrier density.
- Partial current can flow
Insulator & Perfect Insulator
Material with a low charge carrier density
- Minimal current can flow (Insulator)
- No current can flow (Perfect Insulator)
Equation for number of charge carriers per / m^3
n = N / V
n = no. charge carriers / m^3
N = no. charge carriers in material
V = Volume of material
What happens when you heat a thermistor
More electrons become free to move and therefore more current can flow.
What happens if light intensity increases with an LDR?
More electrons are freed and therefore, the conductivity increases.
What happens as energy flows into a material.
More electrons become freed and conductivity increases.
What’s the equation for current?
I = Anev
I = Current (A)
A = Cross-sectional area (m^2)
n = Number of charge carriers / m^3
e = Electron charge (1.6x10^-19)
v = Drift Velocity - (ms^-1)
Describe the motion of electrons
Random motion with an overall drift velocity.
What are charge carriers?
Particles that can carry electrical charge.
What is drift velocity
Average velocity of charge carriers.
What is number density?
no. electrons per m^3
What happens to energy when a charged particle is accelerated?
When a PD accelerates a charged particle the energy transferred is equal to the kinetic energy gained by the particle.
1 Volt
PD between 2 points when a 1C charge passing between the points experiences a change in electric potential energy of 1J
Circuit symbols for these components:
- Cell
- Battery
- Resistor
- Variable resistor
Cell: 2 vertical lines, longer one for positive terminal and shorter for negative terminal.
Battery: Same as cell but more horizontal lines in-between
Resistor: Empty rectangle
Variable resistor: Rectangle with NE arrow through
Circuit symbols for these components:
- LDR
- Thermistor
- Diode
- Ammeter
Voltmeter
LDR: Circle with resistor symbol inside, 2 arrows on top right pointing SW
Thermistor: Rectangle with tick through it
Diode: Play button
Ammeter: A
Voltmeter: V
Circuit symbols for these components:
- Fuse
- Capacitor
- Switch
Fuse: Rectangle with horizontal line through
Capacitor: Same as cell but both lines the same length
Switch: U already know it
What does a Voltmeter do + info
Measures change in Ep across COMPONENT
- Must be In parallel
- Very high resistance so no current flows through
Ammeter
Measures current through a position
- Must be in series
Equation for:
- Work
- EMF
- △ Ep
Work: W = QV
EMF: ε = W/Q
△ Ep: △Ep = 1/2mv^2
Circuit symbols for this components:
- LED (Light emitting diode)
- Play button with 2 arrows on top left pointing NE
IV graphs for these components:
- Resistor
- Filament bulb
- Diode
Resistor - y=x
Filament bulb - f shape
Diode - Flat when -x but exponential increase when +x
