Students should be able to: • use circuit diagrams to construct and check series and parallel circuits that include a variety of common circuit components • describe the difference between series and parallel circuits • explain qualitatively why adding resistors in series increases the total resistance whilst adding resistors in parallel decreases the total resistance • explain the design and use of dc series circuits for measurement and testing purposes • calculate the currents, potential differences and resistances in dc series circuits • problems for circuits which include resistors in series using the concept of equivalent resistance. Students are not required to calculate the total resistance of two resistors joined in parallel. 4.2.3 Domestic uses and safety 4.2.3.1 Direct and alternating potential difference electricity is an ac supply. In the United Kingdom the domestic electricity supply has a frequency of 50 Hz and is about 230 V. Students should be able to explain the difference between direct and alternating potential difference. 34 28 36, 166 4.2.3.2 Mains electricity Most electrical appliances are connected to the mains using three-core cable. The insulation covering each wire is colour coded for easy identification: live wire – brown neutral wire – blue earth wire – green and yellow stripes. 34 29 36, 167
Students should be able to determine speed from a distance–time graph. 4.5.6.1.5 Acceleration The average acceleration of an object can be calculated using the equation: acceleration, a, in metres per second squared, m/s2 change in velocity, ∆v, in metres per second, m/s time, t, in seconds, s An object that slows down is decelerating. Students should be able to estimate the magnitude of everyday accelerations. The acceleration of an object can be calculated from the gradient of a graph. (HT only) The distance travelled by an object (or displacement of an object) can be calculated from the area under a velocity–time graph. Students should be able to: • draw velocity–time graphs from measurements and interpret lines and slopes to determine acceleration • (HT only) interpret enclosed in velocity–time graphs to determine distance travelled (or displacement) • (HT only) measure, when appropriate, the area a velocity–time graph by counting squares. 82-4 67-8 84-6, 205-6 The following equation applies to uniform acceleration: (final velocity)2 – (initial velocity)2 = 2 × acceleration × distance v2 − u2 = 2 a s 82-84 67-8 84-6, 205-6
Students should be able to: • explain the dangers caused by decelerations • (HT only) estimate the forces involved in the deceleration of road vehicles in typical situations on a public road. 4.5.7 Momentum (HT only) 4.5.7.1 Momentum is a property of moving objects Momentum is defined by the equation: momentum = mass × velocity [ p = m v ] momentum, p, in kilograms per second, kg m/s mass, m, in kilograms, kg velocity, v, in metres per second, m/s 90-1 76-8 92-3, 214-6 4.5.7.2 Conservation of momentum In a closed system, the total momentum before an event is equal to the total momentum after the event. This is called conservation of momentum. Students should be able to use the concept of momentum as a model to: • describe and explain examples of momentum in an event, such as a collision • (physics only) complete calculations involving an event, such as the collision of two objects. 90-1 76-8 92-3, 214-6 4.5.7.3 Changes in momentum (physics only) When a force acts on an object that is moving, or able to move, a change in momentum occurs. 90-1 76-8 92-3, 214-6