Question

One joule is approximately equal to:
A.$0.28$Cal
B.$0.32$Cal
C.$0.24$Cal
D.$4.2$Cal

Answer 1

This is the question related to the topic unit conversion. In this question we will use the basic conversion of the unit mentioned above that is $1cal = 4.2J$ to get the value of one joule. We will also use the mathematical unitary method to get the solution.

Complete answer:
According to the question we have to find the value of one joule in the terms of the calories.
As, we know that $1cal = 4.2J$.
From the above unit conversion, we can write as,
$4.2$Joules is equal to the $1$cal.
Then the $1$joule will be equal to the $\dfrac{1}{{4.2}}$calories,
That implies that, $1joule = \dfrac{1}{{4.2}}calories.$
$\Rightarrow 1joule = 0.24calories.$
$\Rightarrow 1J = 0.24cal.$
Hence, the Joule is a unit of energy where $1J = 0.24cal,$ where, $1cal$ is the amount of energy required to raise the temperature of $1$ gram of water by $1^\circ C$.

So, option (C) is the correct answer.

Additional information:
Hence we can say that the calorie was originally defined as the amount of heat required at a pressure of $1$ standard atmosphere to raise the temperature of $1$ gram of water$1^\circ C$. Since $1925$ this calorie has been defined in terms of the joule, the definition since $1948$ being that one calorie is equal to approximately $4.2\;$ joules.

Note:
Here we have seen that the Joule is used as a unit of the heat but also the unit of the work is joule. In the case of work (and also energy), the standard metric unit is the Joule (abbreviated J). One Joule is equivalent to one Newton of force causing a displacement of one meter. In other words, The Joule is the unit of work. A calorie (Cal) is a pre-SI (pre-System International) measurement unit of energy or heat. A kilocalorie is another word for what's commonly called a calorie, so $1,000\;$ calories will be written as $1,000$ Kcals.