Power and efficiency (P7.2) | OCR GCSE Physics A (Gateway Science) — Higher (J249) | KnowledgeSet

Power and efficiency

Physics (Separate Science) · GCSE · OCR · OCR GCSE Physics A (Gateway Science) — Higher (J249) · Specification point · P7.2 · Energy

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P7.2 Power and efficiency

Summary This considers the idea of conservation and dissipation of energy in systems and how this leads to the efficiency. Ways of reducing unwanted energy transfers and thereby increasing efficiency will be explored. Underlying knowledge and understanding Learners should be aware of the transfer of energy into useful and waste energies. They will have an understanding of power and how domestic appliances can be compared. Learners will have knowledge of insulators and how energy transfer is influenced by temperature. They should have an awareness of ways to reduce heat loss in the home. Common misconceptions Learners have the common misconception that energy can be “used up” or that energy is truly lost in many energy transformations. They also tend to have the belief that energy can be completely changed from one form to another with no energy dissipated.

Reference	Mathematical learning outcomes	Mathematical skills
$PM7.2i$	$\text{efficiency}=\frac{\text{useful output energy transfer (J)}}{\text{input energy transfer (J)}}$

Learning outcomes	To include	Maths	Working scientifically	Practical suggestions
$P7.2a describe, with examples, the process by which energy is dissipated, so that it is stored in less useful ways$
$P7.2b describe how, in different domestic devices, energy is transferred from batteries or the a.c. from the mains$	$how energy may be wasted in the transfer to and within motors and heating devices$
$P7.2c describe, with examples, the relationship between the power ratings for domestic electrical appliances and how this is linked to the changes in stored energy when they are in use$			$WS1.3a, WS1.3b, WS1.3c, WS1.3e, WS2a, WS2b$	$Use of a joulemeters to investigate the power output of different electrical appliances. (PAG P5)$
$P7.2d calculate energy efficiency for any energy transfer$		$M1a, M1b, M1d, M2a, M3a, M3b, M3c, M3d$
$P7.2e describe ways to increase efficiency$
$P7.2f explain ways of reducing unwanted energy transfer$	$lubrication and thermal insulation$		$WS1.1b, WS1.1e, WS1.1f, WS1.1g, WS1.1i, WS1.3b$	$Research, design and building of energy efficient model houses. Examination of thermograms of houses.$
$P7.2g describe how the rate of cooling of a building is affected by the thickness and thermal conductivity of its walls (qualitative only)$			$WS1.2a, WS1.2b, WS1.2c, WS1.3a, WS1.3c, WS1.3d, WS1.3e, WS1.3g, WS1.3h, WS1.3i, WS2a, WS2b, WS2c, WS2d$	$Investigation of rate of cooling with insulated and non-insulated copper cans. (PAG P5)$