On a cold day, a shiny metal rod feels colder to the touch than a black plastic rod. Which statement explains this observation?

A.
The metal rod is a better absorber of infra-red radiation than the plastic rod.
B.
The metal rod is a better thermal conductor than the plastic rod.
C.
The metal rod is a worse absorber of infra-red radiation than the plastic rod.
D.
The metal rod is a worse thermal conductor than the plastic rod.
Physics
IGCSE&ALevel
CAIE
Exam No:0625_w18_qp_21 Year:2018 Question No:19

Answer:

B

Knowledge points:

2.3.1.1 Describe experiments to demonstrate the properties of good thermal conductors and bad thermal conductors (thermal insulators)
2.3.1.2 Describe thermal conduction in all solids in terms of atomic or molecular lattice vibrations and also in terms of the movement of free (delocalised) electrons in metallic conductors
2.3.1.3 Describe, in terms of particles, why thermal conduction is bad in gases and most liquids
2.3.1.4 Know that there are many solids that conduct thermal energy better than thermal insulators but do so less well than good thermal conductors
2.3.2.1 Know that convection is an important method of thermal energy transfer in liquids and gases
2.3.2.2 Explain convection in liquids and gases in terms of density changes and describe experiments to illustrate convection
2.3.3.1 Know that thermal radiation is infrared radiation and that all objects emit this radiation
2.3.3.2 Know that thermal energy transfer by thermal radiation does not require a medium
2.3.3.3 Describe the effect of surface colour (black or white) and texture (dull or shiny) on the emission, absorption and reflection of infrared radiation
2.3.3.4 Know that for an object to be at a constant temperature it needs to transfer energy away from the object at the same rate that it receives energy
2.3.3.5 Know what happens to an object if the rate at which it receives energy is less or more than the rate at which it transfers energy away from the object
2.3.3.6 Know how the temperature of the Earth is affected by factors controlling the balance between incoming radiation and radiation emitted from the Earth's surface
2.3.3.7 Describe experiments to distinguish between good and bad emitters of infrared radiation
2.3.3.8 Describe experiments to distinguish between good and bad absorbers of infrared radiation
2.3.3.9 Describe how the rate of emission of radiation depends on the surface temperature and surface area of an object
2.3.4.1 Explain some of the basic everyday applications and consequences of conduction, convection and radiation, including: (a) heating objects such as kitchen pans (b) heating a room by convection

Solution:

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