Question

Choose the correct statement for the following:
(This question has multiple correct answers.)
A) ${50^ \circ }C$ is equal to${122^ \circ }F$ .
B) A clinical thermometer cannot be sterilized using boiling water.
C) Unequal expansion causes cracks in the walls of buildings.
D) Graphite is a bad conductor of heat.

Answer 1

Hint: When a material is heated or exposed to an increase in temperature, the material expands.

Formulae used:
$F = \dfrac{9}{5}C + 32$ --------🡪 (F= temperature in $^ \circ F$, C=temperature in $^ \circ C$ )

Complete solution:
The simple relation between degree Celsius and degree Fahrenheit is given by,
     $F = \dfrac{9}{5}C + 32$ ---------- 🡪(F=temperature in Fahrenheit, C= temperature in Celsius)
 Also, F=122 and C=50 --------------- 🡪(given)
Substituting these values in the formula,
LHS=122 --------🡪 (equation:1)
RHS=$\dfrac{9}{5} \times 50 + 32$
Thus, RHS=$90 + 32 = 122$ ---------- 🡪(equation:2)
Thus, from equation: 1 and equation: 2 we get,
RHS=LHS=122
Thus, ${50^ \circ }C$ is equal to ${122^ \circ }F$ .

Hence, option A is correct.

When a body is heated or exposed to a temperature increase then the body expands and this expansion is termed as thermal expansion. When a body is heated the atoms and molecules absorb the energy. As a result the interatomic and intermolecular distances start increasing. This results in an increase in the dimensions of the body. Thermal expansion if let to happen freely (without any restrictions on the body) the body will not experience any force. However, if restrictions are applied on the body and then the body is heated then the body experiences forces which can be compressive or tensile in nature. If the restrictions are permanent or are applied for a long period of time these forces could damage the body and result in cracks and fracture in the body.
Sterilizing means removing the bacteria or disinfecting. Thermometer due to its use in medical treatment rather diagnosis should be disinfected or sterilized in order to avoid a pandemic as a result.
Clinical thermometers consist of a glass tube filled with mercury (Hg). As mercury is in liquid phase, at room temperature its molecules are already with higher energy than solid mercury molecules. Thus, if we sterilize the thermometer with boiling water which is at a temperature of about 99-100 degree Celsius there will be thermal expansion of mercury but the mercury inside the tube is restricted to expansion(it can expand to a certain limit, i.e. length of the glass tube). So, the expanding mercury will exert pressure on the walls of the glass tube, which would result in breaking the glass and damaging the thermometer.
Thus, boiling water should not be used to sterilize clinical thermometers.

Hence, option B is not correct.

Every object which is exposed to heat and gets heated will undergo thermal expansion. Their relative rates may be very less but they undergo thermal expansion. Even the walls. But as discussed above the restriction could result in pressure application on the body giving arise to the possibility of damage or fracture. Similarly, if a body is undergoing uneven or non-uniform thermal expansion, some parts of the body expand while the others are not expanding. The non-expanding parts behave like restrictions and result in application of forces mostly tensile or opposing like friction. This uneven application of forces on the body results in damaging the body. As a result, cracks may appear as well as chances of fracture are also there.
Thus, unequal expansion of walls causes cracks in the walls of buildings.

Hence, option C is correct.

Thermal conductivity is not a property of non-metals; graphite is a non-metal so it is a bad conductor of heat. Although, due to the presence of free pi-electrons in each sheet it is a very good conductor of electricity. Graphite is an allotrope of carbon and carbon is a non-metal. So, graphite is also a non-metal.
Thus, graphite does not conduct heat.

Hence, option D is correct.

Therefore, the answer to the question is option A, option C and option D.

Note:If a clinical thermometer is sterilized using proper disinfectant the fear of damaging it is not there.
For any object restricted thermal expansion leads to the generation of thermal stresses that can damage the body.
The fact that graphite being non-metal is a good conductor of electricity is due to the free or delocalised pi-electrons that each layer has. Those electrons are only responsible for electric conductivity and not thermal conductivity.