Study Notes on Energy Transfers

Chapter 14: Energy Transfers

1. Energy Stores

  • There are seven important energy stores:

    • Chemical Energy

    • Kinetic Energy

    • Gravitational Potential Energy

    • Elastic Potential Energy

    • Thermal Energy

    • Nuclear Energy

    • Electromagnetic Energy

2. Energy Transfers in Various Situations

a. Bungee Jump

  • Energy Input: Gravitational potential energy at the start of the jump.

  • Energy Transfer: Energy is converted to kinetic energy as the jumper falls, then transformed back to elastic potential energy when the bungee cord stretches.

  • Energy Output: Thermal energy due to air resistance and sound energy during the jump.

b. Oscillating Spring

  • Energy Input: Initial energy provided to compress or stretch the spring.

  • Energy Transfer: Energy oscillates between kinetic and elastic potential energy as the spring moves.

  • Energy Output: Some energy lost as thermal energy due to internal friction and air resistance.

c. Burning Candle

  • Energy Input: Chemical energy from the wax.

  • Energy Transfer: Converts chemical energy into thermal energy and light energy through combustion.

  • Energy Output: Heat energy that warms the surroundings and light energy emitted as illumination.

d. TV Set

  • Energy Input: Electrical energy supplied to the TV.

  • Energy Transfer: Transforms electrical energy into light energy and sound energy.

  • Energy Output: Light energy displayed on the screen and sound energy from the speakers.

e. Nuclear Power Station

  • Energy Input: Nuclear energy from splitting atoms.

  • Energy Transfer: Converts nuclear energy into thermal energy, then into mechanical energy to turn turbines.

  • Energy Output: Electrical energy generated and emitted waste heat.

3. Principle of Conservation of Energy

a. Definition

  • The principle of conservation of energy states that energy cannot be created or destroyed, only converted from one form to another.

b. Efficiency Calculation for a Filament Light Bulb

  • Given: 100 J of energy supplied, 10 J as light energy.

  • Efficiency Formula:
    Efficiency = \frac{Useful\ Energy\ Output}{Total\ Energy\ Input} \times 100

  • Calculation:
    Efficiency = \frac{10\,J}{100\,J} \times 100 = 10\%

c. Energy Transfer for New Energy Efficient Bulb

  • Given: Efficiency of the new bulb = 0.66, energy supplied = 40 J.

  • Useful Energy Transfer Calculation:
    Useful\ Energy\ Output = Efficiency \times Total\ Energy\ Input
    = 0.66 \times 40\,J = 26.4\,J

4. Energy Transfer in a Hairdryer

a. Energy Transfer Description

  • Energy Input: 2000 J of electrical energy.

  • Energy Output: 1500 J of useful kinetic and thermal energy; 500 J wasted as sound and heat.

  • Sankey Diagram:
    (Insert Sankey Diagram representation of energy flow: 2000 J into 1500 J useful energy and 500 J wasted)

b. Efficiency Calculation of Hairdryer

  • Efficiency Formula:
    Efficiency = \frac{Useful\ Energy\ Output}{Total\ Energy\ Input} \times 100

  • Calculation:
    Efficiency = \frac{1500\,J}{2000\,J} \times 100 = 75\%

5. Energy Transfer in a Toaster

a. Total Energy Supplied Calculation

  • Given: Efficiency = 50%, useful energy transferred to bread = 750 J.

  • Finding Total Energy Input:

    • Useful Output: 750 J as heat to bread.

    • Wasted Energy: 450 J (to surroundings) + 300 J (light and sound) = 750 J wasted.

  • Total Energy Supplied Calculation:
    Total\ Energy\ Supplied = Useful\ Energy + Wasted\ Energy = 750\,J + 750\,J = 1500\,J

b. Sankey Diagram for Toaster

  • Sankey Diagram Representation:
    (Insert Sankey Diagram representation based on calculated total energy, dividing into useful and wasted energies)