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Question 18N.2.HL.TZ0.d.ii

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Date November 2018 Marks available [Maximum mark: 4] Reference code 18N.2.HL.TZ0.d.ii
Level HL Paper 2 Time zone TZ0
Command term Determine Question number d.ii Adapted from N/A
d.ii.
[Maximum mark: 4]
18N.2.HL.TZ0.d.ii

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.

Determine the peak current in the primary coil when operating with the maximum number of lamps.

[4]

Markscheme

power = 190 OR 192 «W» ✔

required power = 190 × 100 95 «200 or 202 W» ✔

so 200 240 = 0.83 OR 0.84 «A rms» ✔

peak current = « 0.83 × 2 OR 0.84 × 2 » = 1.2/1.3 «A» ✔

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