OCR.4.1.3
Power is the rate of energy transfer
Energy, Power & Resistance - OCR A-Level Physics
- PowerThe rate of energyThe capacity to do work. Measured in joules (J). transfer. Measured in watts (W). is the rate of energyThe capacity to do work. Measured in joules (J). transfer. Measured in watts (W).
- Three equivalent forms - choose based on what quantities you know.
$$P = IV$$
$$P = I^{2}R$$
$$P = \frac{V^{2}}{R}$$
- Derive $P = I^2R$ by substituting $V = IR$ into $P = IV$.
- Derive $P = V^2/R$ by substituting $I = V/R$ into $P = IV$.
- Brightness of a $lamp = powerThe rate of energy transfer. Measured in watts (W). dissipated. Brighter lamp = higher powerThe rate of energy transfer. Measured in watts (W).$.
Examiner Tips and Tricks
- Brightness of a lamp is determined by its powerThe rate of energy transfer. Measured in watts (W)., not just currentThe rate of flow of chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. Measured in amperes (A)..
- In series, same currentThe rate of flow of chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. Measured in amperes (A). flows - the lamp with higher resistanceThe opposition to currentThe rate of flow of chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. Measured in amperes (A). flow. The ratio of potential difference to current. Measured in ohms (Ω). has more power ($P = I^2R)$ and glows brighter.
Related:Circuits Kirchhoff
Internal Resistance