O-LevelPhysicsMagnetism5054/22 · May/June 2017 · Q76 Marks
Fig. 7.1 shows part of a d.c. electric motor. A coil of wire ABCD is placed between the poles of a magnet. Ends X and Y are connected to a commutator and a battery. [Figure 7.1]
- (a)(i)State why there is a force on side AB of the coil.[1]
- (a)(ii)Describe how the commutator keeps the coil rotating in one direction.[2]
- (b)(i)The current in the motor is 2.0A and the battery has an electromotive force (e.m.f.) of 12V. In a time of 8.0s, the motor does 140J of work. Calculate the energy supplied to the motor in 8.0s,[2]
- (b)(ii)the efficiency of the motor.[1]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (May/June 2017). The mark or mark type is shown in brackets.
- [1] current in coil (at right angles) in a magnetic field (of magnet) or left-hand rule mentioned
- [1] reverses / changes direction of current (in coil)
- [1] reverses current every half turn / when coil is vertical or reverses forces (on side AB / CD) or keeps forces in same direction for wire on one side
- [1] (E = )VIt or 2 × 12 × 8 or E = Pt and P = VI or E = VQ and Q = It
- [1] 190 or 192 J
- [1] 73% or 0.73
Write your answer and get it marked
On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.
Sign up free →