Question

The bimetallic strip made up of aluminium and copper, when heated bends in the direction shown below. Which metal expands more when the two are heated at the same temperature?


(A) Aluminium expands more than copper
(B) Copper expands more than aluminium
(C) Both aluminium and copper expand by the same amount
(D) Neither aluminium nor copper expands

Answer 1

Hint: We know that metal expands when heated. Length, surface area and volume will increase with temperature. The scientific term for this is thermal expansion. The degree of thermal expansion varies with different types of metal. The expansion (or contraction) of any material is due to the kinetic energy of its atoms. When a material is heated, the increase in energy causes the atoms and molecules to move more and to take up more space that is, to expand. Thermal expansion is the tendency for a material to change its characteristics due to external temperature. At extremely low temperatures, silicon and germanium expand with cooling rather than heating.

Complete step by step answer
We know that a bimetallic strip is used to convert a temperature change into mechanical displacement. The strip consists of two strips of different metals which expand at different rates as they are heated, usually steel and copper, or in some cases steel and brass. The bimetallic strip is made of two metal strips, stuck together. One of the metals expands much more than the other when they are heated. This causes the strip to bend. A bi-metallic strip can be used as a sensor in a thermostat.
Bimetal strips are used in miniature circuit breakers to protect circuits from excess current. A coil of wire is used to heat a bimetal strip, which bends and operates a linkage that unlatches a spring-operated contact. This interrupts the circuit and can be reset when the bimetal strip has cooled down. When this bimetallic strip is heated, the brass expands more than the steel and the strip curves with the brass on the outside. If the strip is cooled, it curves with the steel on the outside. Bimetallic strips are used as switches in thermostats.
The outer edge of the curve is longer as aluminium expands more than copper, if both are heated at the same temperature.

Hence, we can say that Aluminium expands more than copper. So, the correct answer is option A.

Note: We know that thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions. Temperature is a monotonic function of the average molecular kinetic energy of a substance. Thermal expansion is caused when seawater expands because of the higher temperature of the water. Since the oceans absorb heat from the atmosphere, when the atmosphere becomes warmer so will the oceans. The increased volume will cause the level of the water in the oceans to rise. Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions. Temperature is a monotonic function of the average molecular kinetic energy of a substance.