Physics Electricity Unit 1

Current

the flow of electrons in a conductive material

unit - Amperes (A)

Voltage

the force behind electrons

the potential difference between two points

unit - Volts (V)

→ V = C/J

Kilowatt Hours

→ kW/h

what electrical energy is measured in

used to calculate costs/price electricity

Watts

One joule per second

→ W = J/sec

Charge

the property of matter that causes electric effects

unit - electric charge (Q) in Coulombs (C)

Frequency

how many times current changes direction in one second

unit - Hertz (Hz)

Charge Separation

process that transfers electrons from one substance to another

→ charge imbalance

Electrical Potential Energy

the energy of a charged particle because of its position in a circuit

→ the energy used up by loads

Unit - Joules (J)

U = QV

Potential Energy

the measure of electrical potential energy each coulomb of charge carries from the battery

→ V = E/Q

AC Current

• constantly switching directions

• sine wave

• voltage oscillates

  Frequency → 50/60 Hz

DC Current

• flows in one direction ONLY

• voltage stays constant

  Frequency → 0 Hz

Voltmeter

measures the electrical potential difference between two points

→ used to find the amount of voltage used by a load

→ placed in parallel to the load

Unit - Volts (V)

Ammeter

measures the electrical current flowing through the circuit

→ used to find the current

→ placed in series in the circuit

Unit - Amperes (A)

Ampere

the unit of current (A)

→ one coulomb per second

Coulomb

the measurement of electrical charge

Volts

the unit of voltage (V)

→ how ‘strong’ the flow is

Diode

non-oh mix resistor where current flows one way

LED

→ light emitting diode

lights up when current flows

Potentiometer or Variable Resistor

ohmic resistor whose voltage can change

→ forms adjustable voltage divider

LDR

→ Light Dependant Resistor

semiconductor whose resistance changes based on the light level (lux)

Thermistor

→ thermal resistor

semiconductor whose resistance changes based on temperature

Transducer

electrical component which receives an input signal in one form of energy and converts it

Parallel Circuits

components of a circuit are connected across common points, providing multiple pathways

→ current (A) is split proportionally at each junction

→ voltage (V) is the same between pathways

→ total resistance is lower than individual resistances

Series Circuits

all components of a circuit are connected in a single loop

→ current (A) is equal throughout the circuit

→ voltage (V) is split proportionally between loads

→ total resistance is the sum of resistances

Ohm’s Law

V = IR

I = V/R

R = V/I

Resistance

the measure of opposition to the flow of current in a circuit that controls

Unit - Ohms (Ω)

Equivalent Resistance

the total amount of resistance in a circuit

→ Req or RT

Unit - Ohms (Ω)

Equivalent Resistance in Series

Req = R1 + R2 …

Equivalent Resistance in Parallel

1/Req = 1/R1 + 1/R2 …

or

Req = (R1 x R2)/(R1 + R2)

Potential Divider

a series circuit that controls the amount of voltage using 2 resistors

→ proportional to V=IR

→ Vout = Vin x (R2/(R1 + R2))

Power / Wattage

Rate of transfer of electrical energy

→ measure of energy per charge

Unit - Watts (W)

Watt’s Law

P = VI

Neutral Wire

the wire that carries current from the load back to the power source

Active Wire

the wire that carries current and voltage to the load

Earth Wire

the wire which provides a low-resistance pathway to the earth in case of too much current

Fuse

a thin, low resistance wire which melts if too much current passes, breaking the circuit

Circuit Breaker

a device which interrupts current if there is too much and forms an electromagnet which trips the switch and breaks the circuit