DP Physics (last assessment 2024)

Question 18N.3.SL.TZ0.2c

Date	November 2018	Marks available	[Maximum mark: 2]	Reference code	18N.3.SL.TZ0.2c
Level	SL	Paper	3	Time zone	TZ0
Command term	Suggest	Question number	c	Adapted from	N/A

[Maximum mark: 2]

18N.3.SL.TZ0.2c

In an experiment to measure the specific latent heat of vaporization of water L_v, a student uses an electric heater to boil water. A mass m of water vaporizes during time t. L_v may be calculated using the relation

${L_v} = \frac{{VIt}}{m}$

where V is the voltage applied to the heater and I the current through it.

(c)

A student suggests that to get a more accurate value of L_v the experiment should be performed twice using different heating rates. With voltage and current V₁, I₁ the mass of water that vaporized in time t is m₁. With voltage and current V₂, I₂ the mass of water that vaporized in time t is m₂. The student now uses the expression

${L_v} = \frac{{\left( {{V_1}{I_1} - {V_2}{I_2}} \right)t}}{{{m_1} - {m_2}}}$

to calculate L_v. Suggest, by reference to heat losses, why this is an improvement.

[2]

Markscheme

heat losses will be similar / the same for both experiments

heat loss presents systematic error ✔

taking the difference cancels/eliminates the effect of these losses

use a graph to eliminate the effect ✔

Syllabus sections

Core

Core » Topic 1: Measurements and uncertainties » 1.1 – Measurements in physics

Core » Topic 1: Measurements and uncertainties

Question 18N.3.SL.TZ0.2c

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