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 where V is the voltage applied to the heater and I the current through it.
Outline why, during the experiment, V and I should be kept constant.
to provide a constant heating rate / power OR to have proportional to
Outline whether the value of L_v calculated in this experiment is expected to be larger or smaller than the actual value.
due to heat losses «VIt is larger than heat into liquid» calculated will be larger
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 V_1, I_1 the mass of water that vaporized in time t is m_1. With voltage and current V_2, I_2 the mass of water that vaporized in time t is m_2. The student now uses the expression
to calculate L_v. Suggest, by reference to heat losses, why this is an improvement.
heat losses will be similar / the same for both experiments OR heat loss presents systematic error taking the difference cancels/eliminates the effect of these losses OR use a graph to eliminate the effect
