Electricity and Magnetism - Electrical Energy

Lesson 1: Electricity and Magnetism - Electrical Energy (March 31st 2025)

In this lesson, we explore electrical energy, defined as energy produced by the flow of electric charge, powering devices and systems.

  • Power (P) is the rate at which energy is transformed.

  • Electrical power is the rate at which electrical energy is produced or consumed.

  • Equation: P=ΔEΔtP = \frac{\Delta E}{\Delta t}

    • P = Power

    • ΔE\Delta E = Change in energy

    • Δt\Delta t = Change in time

  • Power is expressed in watts (W).

  • Electrical devices have varying power ratings.

Example Problem: Power Calculation

  • Problem: Calculate the power required to charge a cellphone if 740 J of energy is transferred in 1.0 min.

  • Solution: P=740 J60 s=12 WP = \frac{740 \text{ J}}{60 \text{ s}} = 12 \text{ W}

  • Statement: The power required to charge the cellphone is 12 W.

Measuring Electrical Energy

  • Electrical energy is measured in kilowatt hours (kWh).

  • 1 kWh = 3.6 million joules.

  • A typical home in Ontario uses 1000 kWh of electrical energy each month.

Example Problem: Calculating Energy

  • Problem: Calculate the energy needed by a 35 W halogen light bulb that operates for 240 h. Give the answer in both joules and kilowatt hours.

  • Solution: ΔE=(35 W)(864,000 s)=3.024×107 J\Delta E = (35 \text{ W}) (864,000 \text{ s}) = 3.024 \times 10^7 \text{ J}, 3.024×107 J×1 kWh3.6×106 J=8.4 kWh3.024 \times 10^7 \text{ J} \times \frac{1 \text{ kWh}}{3.6 \times 10^6 \text{ J}} = 8.4 \text{ kWh}

Production of Electricity

  • Mechanical, thermal, and radiant energy are transformed into electrical energy in power plants.

  • Power plant technologies vary in efficiency and impact.

  • Improving power plant efficiency can decrease resource use.