2.2.3. Melting, boiling and evaporation
A subsection of Physics, 5054, through 2. Thermal physics
Listing 10 of 166 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
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is a diagram of a soldering iron. Solder is a mixture of metals used to make a permanent contact between electrical wires. heating element metal tip The heating element raises the temperature of the metal tip. When solder is placed against the tip, the solder melts over the wires to be joined. When the solder cools, it solidifies and the permanent connection is made. The working temperature of the metal tip is 380 °C. The boxes in show two materials and some different melting points. melting point 1000 °C solder metal of the metal tip 380 °C 200 °C 20 °C 0 °C material On , draw a line from the metal of the metal tip and a line from the solder to a suitable melting point for each. The heating element is rated at 24 V, 3.3 A. The heating element is switched on. The temperature of the metal tip rises from 20 °C to 320 °C in the first 10 s. Calculate the electrical energy supplied to the heating element in the first 10 s. energy = The metal tip is made of copper and has a mass of 2.3 g. The specific heat capacity of copper is 0.39 J / (g °C). Calculate the thermal energy gained by the metal tip in the first 10 s. thermal energy = Describe, in terms of free electrons, the process by which heat transfers through the metal tip. Heat is lost from the metal tip by convection in the air. Explain how convection occurs in the air. The temperature of the metal tip is measured with a thermocouple. In the space below, draw a labelled diagram of a thermocouple. Mark with a letter H the part of the thermocouple that is placed on the metal tip. State two reasons why a thermocouple thermometer is suitable for measuring how the temperature of the metal tip varies during the first 10 s. 1. 2.
5054_s19_qp_22
THEORY
2019
Paper 2, Variant 2
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Questions Discovered
166