Question

What unit is equivalent to the coulomb?
A. ampere-second
B. joule per volt
C. watt per ampere
D. watt per volt

Answer 1

Hint: Coulomb is the unit of charge. The electric current is the charge flowing through a circuit per unit time. Therefore, the units of current, charge and time are related to each and unit of coulomb can be calculated from their relation.

Complete Step-by-Step solution:
Electric charge is the property of matter by virtue of which it experiences a certain force when it is placed in an electric or magnetic field. Charge can either be positive or negative. Opposite charges attract each other whereas like charges repel each other. We can measure charge on a body in terms of its S.I. unit which is Coulomb (C). The symbol for charge is q.
The flow of electric charge produces an electric current. Electric current is defined as charge flowing through a wire per unit time. Its symbol is I. The S.I. unit of current is ampere (A). Mathematically,
$$I={\displaystyle \frac{q}{t}}$$
Therefore, we can express charge in terms of current and time as follows:
$$q=I\times t$$
Writing this equation in terms of the units of various quantities, we get
$$1C=1A\times 1s$$
This equation defines 1 coulomb as the amount current flowing through a circuit in 1s. Therefore, 1 coulomb is equivalent to 1 ampere-second. In other words, coulomb and ampere-second are both the units of charge and imply the same meaning.
Hence, the correct answer is option A.

Note: Joule is the unit of heat and has no direct relation with charge due to which option B is wrong. By relating the various equations between the quantities, the relation between units can be found but all units must be in the same system. In this question, all units are in S.I. units.