IB Physics SL B.1.10 Thermal transfer mechanisms

Choose conduction, convection or radiation in real devices and explain the design decision or pathway that transfers energy.

Exam points

explain a design choice with a mechanism, such as trapped air reducing conduction and stopping convection
state that energy from a hot core reaches the surface mainly by conduction through solid material
define thermal radiation as infrared electromagnetic emission, even when no medium is present

[Maximum number: 3]

An electrically heated pad is designed to keep a pet warm.

The pad is heated using a resistor that is placed inside the pad. The dimensions of the resistor are shown on the diagram. The resistor has a resistance of $4.2 \Omega$ and a total length of 1.25 m .

Figure for Question B.1.10—Thermal transfer mechanisms question 1 — IB Physics SL

When there is a current in the resistor, the temperature in the pad changes from a room temperature of $20^{\circ} \mathrm{C}$ to its operating temperature at $35^{\circ} \mathrm{C}$ .

The design of the pad encloses the resistor in a material that traps air. The design also places the resistor close to the top surface of the pad.

Explain, with reference to thermal energy transfer, why the pad is designed in this way.

All question bank results loaded

B.1.10—Thermal transfer mechanisms question 1