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Question 19M.1.HL.TZ2.21

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Date May 2019 Marks available [Maximum mark: 1] Reference code 19M.1.HL.TZ2.21
Level HL Paper 1 Time zone TZ2
Command term Question number 21 Adapted from N/A
21.
[Maximum mark: 1]
19M.1.HL.TZ2.21

A train approaches a station and sounds a horn of constant frequency and constant intensity. An observer waiting at the station detects a frequency fobs and an intensity Iobs. What are the changes, if any, in Iobs and fobs as the train slows down?

[1]

Markscheme

D

Examiners report

An unusual way of considering the Doppler effect, this had a very low discrimination index with the most popular answer A when D was correct. It is likely the candidates have confused what the train is producing – a constant intensity sound – and what the observer hears, Io, where the intensity is going to increase as the train approaches. This immediately eliminates options A and C.

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