Question 18N.2.HL.TZ0.2d.i
| Date | November 2018 | Marks available | [Maximum mark: 2] | Reference code | 18N.2.HL.TZ0.2d.i |
| Level | HL | Paper | 2 | Time zone | TZ0 |
| Command term | Outline | Question number | d.i | Adapted from | N/A |
A lighting system consists of two long metal rods with a potential difference maintained between them. Identical lamps can be connected between the rods as required.
The following data are available for the lamps when at their working temperature.
Lamp specifications 24 V, 5.0 W
Power supply emf 24 V
Power supply maximum current 8.0 A
Length of each rod 12.5 m
Resistivity of rod metal 7.2 × 10–7 Ω m
A step-down transformer is used to transfer energy to the two rods. The primary coil of this transformer is connected to an alternating mains supply that has an emf of root mean square (rms) magnitude 240 V. The transformer is 95 % efficient.
Outline how eddy currents reduce transformer efficiency.
[2]
«as flux linkage change occurs in core, induced emfs appear so» current is induced ✔
induced currents give rise to resistive forces ✔
eddy currents cause thermal energy losses «in conducting core» ✔
power dissipated by eddy currents is drawn from the primary coil/reduces power delivered to the secondary ✔
