2. Thermal physics
A section of Physics, 5054
Listing 10 of 446 questions
Describe two differences between boiling and evaporation. 1. 2. Explain, using ideas about molecules, why thermal energy is needed to boil a liquid. In one type of bathroom shower, cold water passes through a metal pipe which contains an electric heater. The cold water is heated and emerges from the shower head. The temperature of the cold water before heating is measured and the hot water emerging from the shower in 1.0 minute is collected in a container. Measurements and other data are: temperature of water before heating = 16 °C temperature of water after heating = 37 °C volume of water collected in 1.0 minute = 4.6 × 10−3 m3 specific heat capacity of water = 4200 J / (kg °C) density of water = 1000 kg / m3 Calculate the mass of water leaving the shower in 1.0 s. mass = Calculate the thermal energy gained by the water in 1.0 s. energy = To calculate the efficiency of the shower, the value in and the value of one other quantity are needed. 1. State what other quantity is needed. 2. Describe how these two values are used to calculate the efficiency of the shower. The metal pipe that contains the electric heater is earthed. Explain why this is necessary.
5054_s18_qp_21
THEORY
2018
Paper 2, Variant 1
View
A hot steel rod is cooled by plunging it into cold water, as shown in . steel rod The steel rod has a mass of 2.0 kg and is initially at a temperature of 500 °C. It cools to 50 °C when placed in the water. The specific heat capacity of steel is 460 J / (kg °C). Calculate the thermal energy lost by the steel rod as it cools to 50 °C. thermal energy = A small mass of water boils when the rod is placed in the water. The remaining water then cools to room temperature and some of it evaporates. In both boiling and evaporation, water molecules escape into the air. State one way in which boiling is different from evaporation. The rate of evaporation decreases as the water cools. Explain why this happens, using ideas about molecules.
5054_s21_qp_21
THEORY
2021
Paper 2, Variant 1
View
Questions Discovered
446