Unit 1: Electricity and Energy Flashcards
Electrons
Orbit nucleus and have a negative charge
Like Charges
Repel
Opposite Charges
Attract
Electric Charge
Given the symbol Q. Measured in Coulombs(C)
Charge of an Electron
-1.6 x10-19C
In an electric field electrons
Accelerate towards a positive voltage and away from a negative voltage
Electric Field Line
Diagram which shows the direction of the force a small positive charge would experience
Field Line Rules
Lines are continuous
Lines never touch or cross
Closer the lines are to each other, the stronger the electric field
Current
Amount of charge flowing through a conductor each second. GIven symbol I and measured in Amperes(A)
Measuring Current
Use an ammeter
Potential Difference (Voltage)
The amount of energy transferred per coulomb of charge. Given symbol V and measured in Volts(V)
Direct Current (d.c.)
Steady voltage provided causing a steady flow of electrons in one direction. Appears as straight line on oscilloscope
Example: Batteries
Alternating Current (a.c.)
Mains or signal generator provides a voltage which changes with a constantly changing direction resulting in electrons moving backwards and forwards
Mains Voltage
Average - 230V
Peak - 325 V
Mains Frequency
50 Hz
Uniform Field
One of Constant Strength
Resistance
Property of a conductor to oppose current. Given symbol R and measured in Ohms(Ω)
Ohm’s Law
Current in the resistor is proportional to the voltage across it
Voltage Divider Circuit
2 or more resistors are connected in series, sharing the voltage between them
Non-Ohmic Conductors
Current through the conductor is NOT proportional to the voltage across it. Example - Light Bulb
Light Bulb Resistance
As temperature of light bulb gets bigger its resistance increases
Diode
Semi-conductor that only allows current to flow in one direction. Only conducts when more than 0.7 V is applied
Cell
Transfers chemical energy to electric energy providing electric energy to make charge move in a circuit
Battery
Transfers chemical energy to electric energy providing electric energy to make charge move in a circuit
Resistor
Made from various compounds or resistance wire, designed to limit the current in a circuit
Variable Resistor
Used to vary the current size in a circuit
Fuse
Made with a wire which melts when the current exceeds a limit, designed to break the circuit to protect other components
Lamp
Transfers electric energy into light (and heat)
Motor
Transfers electric energy into kinetic energy
Voltmeter
Measures the voltage across a component
Ohmmeter
Measures the resistance of a component
Series Circuit
All the components are in a single loop
IS=I1=I2=…
VS=V1+V2+…
RT=R1+R2+…
Parallel Circuit
There are junctions and branches. More than one path for current to flow
VP=V1=V2=…
IP=I1+I2+…
1/Rp= 1/R1 + 1/R2+ 1/R3…
Solar Cell
Transfers light energy to electric energy
Microphone
Transfers sound energy into electric energy
Thermocouple
Transfers heat energy to electric energy
Light Dependant Resistor (LDR)
When exposed to light its resistance decreases
Thermistor
When heated its resistance decreases
Relay Switch
When current is passed through it , it closes a metal switch completing a second circuit
Capacitor
Device that stores charge
Bipolar Transistor
When voltage between base and emitter > 0.7V it conducts along the collector as well / turns on
Electrical Switch
MOSFET
When voltage between gate and source >2V conducts along drain-source/turns on
Electrical Switch
Energy
Given symbol E. Measured in Joules(J)
Power
Energy transferred per second. Given symbol P. Measured in Watts (W)
Types of Energy
Heat
Light
Sound
Electric
Gravitational Potential
Nuclear
Elastic
Chemical
Law of Conservation of Energy
Energy can not be created or destroyed but it can be converted ir transferred from one form to another
Potential/Kinetic Conservation Equation
v = √2gh
Electromagnetic Induction
A changing magnetic field around a coil of wire unduces a potential difference
Increasing Induced Potential Difference/Current
Increase magnetic field strangth
Increase speed of movement
Increase number of turns on the coil
Temperature
Measure of the kinetic energy of individual particles in the material. Given symbol T and measured in Degrees Celcius (ºC) or Kelvin
Heat Energy
Measure of the combined kinetic energy of all the particles in the material
Specific Heat Capacity
Energy required to change the temperature of 1kg of a material by 1ºC. Given symbol c and measured in Jkg-1ºC-1
Specific Latent Heat of Fusion
Energy required to change 1kg of solid at its melting point to 1kg of liquid. Given symbol lf and measured in Joules per Kilogram (Jkg-1)
Specific Latent Heat of Vaporisation
Energy required to change 1kg of liquid at is boiling point to 1kg of gas. Given symbol lv and measured in Joules per Kilogram (Jkg-1)
Pressure
Force per unit area. Measured in Pascals (Pa) and given symbol P
Kinetic Theory
Gas made of atoms and molecules
Atoms and molecules move around randomly in all directions
Atoms and molecules collide elastically with each other and walls of container, exerting a small force
As temperature of atoms and molecules increases so does their kinetic energy
Air Pressure
Sum of forces over area of a container or substance. Atmosphere causes 100kPa
Boyle’s Law
If the volume of a gas is halved its pressure doubles (assuming constant mass and temperature)
P1 x V1 = P2 x V2
Converting Celcius to Kelvin
Add 273
Absolute Zero
-273ºC or 0K
Pressure Law
If temperature (in kelvin) of gas is doubled its pressure doubles (assuming constant mass and volume)
P1/T1 = P2/T2
Charles’ Law
If temperature (in kelvin) of a gas is doubled its volume doubles (assuming constant mass and pressure)
V1/T1 = V2/T2
General Gas Law
P1V1/T1 = P2V2/T2
Kinetic Theory - P+V
As volume increases particles move further apart meaning less frequent collisions with the walls of the container
Total Force Decreases
Area of walls increases
P=F/A so pressure decreases
Kinetic Theory - P+T
As temperature increases particles’ kinetic energy increases and they speed up. Means more frequent collisions, each with a greater force
Total Force increases
P=F/A so pressure increases
Kinetic Theory - V+T
As temperature rises the kinetic energy of particles increases. Means more frequent collisions, each with a greater force
Volume must increase to reduce number of collision so pressure is unchanged
