Question

Material Soda-lime glass Coef of Thermal Expansion 9.0 x 10-6°C 1 23.8 x 10 6°C 4.9 x 100°C Tin Molybdenum A glass jar is tightly capped with either a tin or molybdenum lid. The coefficient of thermal expansion for three materials are shown above. Which of the following combinations of materials and heating or cooling would result in the lid loosening • cooling a soda-lime glass jar with a tin lid cooling a soda-lime glass jar with a molybdenum lid heating a soda-lime glass jar with molybdenum lid none of the above

Answer 1

Coefficient of thermal expansion of the material is the measure of fractional change in size of an object per degree change in temperature.

We need choose the option which leads to loosening of lid upon heating or cooling.

1st option: cooling soda lime glass jar with tin lid.

Cooling tends to decrease the size of an object.

Effect of cooling on size will be larger in tin lid as its coefficient of thermal expansion is greater than soda lime glass.

So the size of tin lid contracts more than the size of the soda lime glass jar resulting in tightening of lid on the soda lime glass jar when cooled. So this combination is incorrect.

2nd option: cooling a soda lime glass jar with molybdenum lid.

Effect of cooling on the size will be larger on the soda lime glass jar as it has larger coefficient of thermal expansion than molybdenum lid.

So the size of the soda lime glass jar contacts more than the size of the molybdenum lid resulting in losening of the lid when cooled. this combination is correct.

3rd option: heating a soda lime glass jar with molybdenum lid.

Heating tends to increase the size of an object.

Effect of heating on the size of object will be greater on the soda lime glass jar as it has greater cofficient of thermal expansion than the molybdenum lid.

so the size of the soda lime glass jar expand more than the size of the molybdenum lid resulting in tightening of lid on the glass jar when heated. So option 3 is incorrect.