DP Physics (last assessment 2024)

Question 18N.2.HL.TZ0.b

Date	November 2018	Marks available	[Maximum mark: 2]	Reference code	18N.2.HL.TZ0.b
Level	HL	Paper	2	Time zone	TZ0
Command term	Calculate	Question number	b	Adapted from	N/A

[Maximum mark: 2]

18N.2.HL.TZ0.b

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

Calculate the maximum number of lamps that can be connected between the rods. Neglect the resistance of the rods.

[2]

Markscheme

current in lamp = $\frac{5}{{24}}$ «= 0.21» «A»

n = 24 × $\frac{8}{{5}}$ ✔

so «38.4 and therefore» 38 lamps ✔