Energy changes in a system, and in the ways energy is stored before and after such changes — WJEC GCSE Physics
In summary: Energy changes in a system, and in the ways energy is stored before and after such changes is a key topic in WJEC GCSE Physics. Key exam tip: Always state the formula being used before substituting values.
Exam Tips for Energy changes in a system, and in the ways energy is stored before and after such changes
- Always state the formula being used before substituting values.
- Ensure all units are in SI base units (e.g., mass in kg, distance in m) before calculating.
- For extended writing questions, clearly link the energy store changes to the specific physical process described.
- Remember that power is a rate; if the time is not provided, check if it can be derived from other given data.
Common Mistakes
- Confusing specific heat capacity with specific latent heat in calculations.
- Failing to convert units (e.g., cm to m for extension or g to kg for mass) before performing calculations.
- Incorrectly identifying the 'distance' in the work done formula as the total distance traveled rather than the distance along the line of action of the force.
- Misinterpreting the change in internal energy during a change of state.
Marking Points
- Correct identification of energy store changes in common scenarios like objects projected upwards or moving vehicles.
- Accurate application of the kinetic energy formula E_k = 0.5mv^2.
- Correct calculation of gravitational potential energy using E_p = mgh.
- Accurate use of the elastic potential energy formula E = 0.5kx^2.
- Correct application of the work done formula W = Fd.
- Accurate calculation of energy changes using specific heat capacity (Q = mcΔT) and specific latent heat (Q = mL).
- Correct calculation of electrical energy transfer using E = QV and E = Pt.
- Correct definition and calculation of power as the rate of energy transfer.
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