2.3. Transfer of thermal energy
A subsection of Physics, 5054, through 2. Thermal physics
Listing 10 of 65 questions
a shows a room heater. b is a diagram of the electric circuit of the heater. switch A live neutral switch B a b The fuse has not been drawn on the circuit diagram in b. On b, draw the symbol for a fuse in the correct position. State the part of the room heater to which the earth wire is connected. The earth wire reduces the chance of an electric shock if a fault develops in the room heater. 1. State one fault that causes an electric shock when a person uses the room heater without an earth connection. 2. Explain how using an earth connection prevents an electric shock. This type of room heater is very efficient. Explain what this means. The room heater is a convector heater. Describe and explain how thermal energy passes around a room by convection. shows the power output of the room heater when each switch is closed. power / W switch A only closed switch B only closed both switches closed Determine the power output of the room heater when only switch B is closed. power output = The room heater is used with both switches closed for 2.5 hours. Calculate the energy output of the room heater 1. in kilowatt-hours, energy = kW h 2. in joules. energy = J
5054_s12_qp_21
THEORY
2012
Paper 2, Variant 1
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A student uses a mobile phone. He is concerned that the energy of the radio waves may cause a temperature rise in his brain. To investigate this effect, he calculates and tries to measure the heating effect of the phone on a nearby glass beaker of water. The phone is used for 360 s when next to a glass beaker containing 50 g of water. Calculate the number of pulses of radio waves produced during the phone call, the total energy of the radio waves emitted during the phone call, the maximum temperature rise produced in 50 g of water if all of the energy calculated in is absorbed by the water. The specific heat capacity of water is 4.2 J/(g °C). The manufacturer gives the input power of the phone as 0.20 W. Calculate the energy supplied by the battery when the phone is used for 360 s. Calculate the fraction of the energy supplied by the battery that is converted into radio wave energy during the phone call. The student uses the mercury-in-glass thermometer shown in . He does not detect any temperature rise in the water in the beaker when the phone is used. Describe how you would check the 0 °C and 100 °C points on the thermometer. Explain why the thermometer is not sensitive enough to detect the temperature rise. State and explain one change that will make a mercury-in-glass thermometer more sensitive. –10 °C pulse of radio waves Information from manufacturer time constant input power 0.20 W The mobile phone emits pulses of radio waves. Each pulse of waves has energy 0.00012 J. There are 216 pulses of waves in 1.0 s
5054_w05_qp_2
THEORY
2005
Paper 2, Variant 0
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Questions Discovered
65