Consider supporting us on Patreon. Help us keep revisedeck free.
9. Electricity
A section of Physics, 9702
Listing 10 of 370 questions
The current I in a metal wire is given by the expression I = Anve. State what is meant by the symbols A and n. A: n: The diameter of a wire XY varies linearly with distance along the wire as shown in . X d d Y current I current I drift speed vx There is a current I in the wire. At end X of the wire, the diameter is d and the average drift speed of the free electrons is vx. At end Y of the wire, the diameter is d 2 . On , sketch a graph to show the variation of the average drift speed with position along the wire between X and Y. vx 2vx 3vx 4vx 5vx average drift speed X Y position along wire
9702_w18_qp_22
THEORY
2018
Paper 2, Variant 2
View
State what is meant by an electric current. Define electric potential difference (p.d.). A power supply of electromotive force (e.m.f.) 8.7 V and negligible internal resistance is connected by two identical wires to three filament lamps, as shown in . 0.30 A power supply 8.7 V connecting wires (not to scale) The power supply provides a current of 0.30 A to the circuit. The filament lamps are identical. The I–V characteristic for one of the lamps is shown in . 0.20 0.30 0.10 0.40 1.0 2.0 3.0 4.0 V / V I / A Show that the resistance of each connecting wire is 2.0 Ω. The resistivity of the metal of the connecting wires does not vary with temperature. On , sketch the I–V characteristic for one of the connecting wires. Calculate the power loss in one of the connecting wires. power = W Some data for the connecting wires are given below. cross-sectional area = 0.40 mm2 resistivity = 1.7 × 10−8 Ω m number density of free electrons = 8.5 × 1028 m−3 Calculate 1. the length of one of the connecting wires, length = m 2. the drift speed of a free electron in the connecting wires. drift speed = m s−1
9702_m16_qp_22
THEORY
2016
Paper 2, Variant 2
View
The current in a filament lamp decreases. State and explain how the resistance of the lamp changes. A cylindrical wire has length L and resistance R. The total number of free electrons (charge carriers) contained in the volume of the wire is N. Each free electron has charge e. The potential difference between the ends of the wire is V. Determine expressions, in terms of some or all of the symbols e, L, N, R and V for: the current in the wire current = the average drift speed of the free electrons average drift speed = the average time taken for a free electron to move along the full length of the wire. time taken =
9702_s23_qp_22
THEORY
2023
Paper 2, Variant 2
View
Questions Discovered
370