Current Electricity Unit Test

What is current electricity?

• The flow of electrons around a circuit

• Electrons in a circuit flow out of the negative and back into the positive terminal

Power source

• Gives energy to the circuit by pushing electrons

• Positive (+) and negative (-) terminal

• Ex. battery, power outlet

Conductors (wires)

• Path for current to flow

• Carries the electrons

Load

• Device that uses electrical energy and converts it into another form (light, heat, motion)

• Ex. light bulb, heater, blender

Switch

• Controls the flow of electricity

• Open switch (off): circuit is broken → current stops

• Closed switch (on): circuit is complete → current flows

Fuse / circuit breaker (optional)

• Safety devices stop the current if it’s too strong (prevents fires or damages)

Complete circuit

Has a power supply and load connected in a circuit

Controlled circuit

Has a switch

Fused circuit

Has a fuse

Short circuit

Has wires but no load (very dangerous)

Voltage (V) - potential difference

• Unit: volt

• Measures electrical potential difference

  • Difference in energy from positive side (high potential) and negative side (low potential)

  • Electrons follow from the negative to the positive side because of the difference in energy

  • Bigger the difference, faster things move

Current (I)

• How many coulombs pass a point per second

• Unit: ampere (A)

  • 1 amp = 1 coulomb / second

• Measures flow of electric charge (how many electrons are passing a point every second [flow rate])

Resistance (R)

• Unit: Ohm (Ω)

• Measures how much a material resists flow

Power (P)

• Unit: watt (W)

• Measures the rate of energy being used or made (speed)

Energy (E)

• Unit: kilowatt-hours (kWh) or Joules (J)

  • J = power (watts) x seconds

  • kWh = kW x h

  • 1 kWh = 3,600,000 J

• Measures total electricity used over time

Voltmeter

Measures voltage (pressure between two points), placed in a parallel circuit

Ammeter

Measures amount of current flowing past a single point, placed in series circuit

Series circuit rules

• One path for current to flow

• Circuit broken at any point → current stops flow

• Light bulb added → dimmer

• Ex. christmas lights

Voltage in series

• Shared amongst components

• V = V1 + V2 + V3…

Current in series

• Constant in all parts

• I = I1 = I2 = I3…

Resistance in series

• Sum of individual resistances

• R = R1 + R2 + R3…

Parallel circuit rules

• Multiple paths (branches)

• One path breakers, others are not affected

• Light bulb added → brightness stays the same

• Ex. house lighting

Voltage in parallel

• Constant in all parts

• V = V1 = V2 = V3…

Current in parallel

• Shared amongst components

• I = I1 + I2 + I3…

Resistance in parallel

• 1/R = 1/R1 + 1/R2 + 1/R3…

• Lower resistance → higher power

Series and parallel rules

• Power: P = Vt x It

• Energy: E = Pt x T

Ohm’s law

V = I x R

Power efficiency

• Efficiency = (useful / total power) x 100%

  • Useful = watts used for converting (load)

  • Total = total watts

  • Wasted = total - useful

Formula triangles

• V / I x R

• P / I x V

• E / P x t