Question

Which is the best instrument for testing the state of charge of a car battery?
A. Voltmeter
B. Ammeter
C. Voltameter
D. Hydrometer

Answer 1

A battery is a power source that contains one or more electrochemical cells whose chemical reactions produce flows of electrons in a circuit. so that the battery is used in flashlights, mobile phones, cars, etc., From the above question, we need to know about the instrument used to test the state of charge (SoC) of the car battery.

Complete step-by-step solution:
State of Charge (SoC) in the battery is generally meant by the level of charge of the battery relative to its full capacity. It is usually indicated in percentage ranges from $0\%$ to $100\%$.
State of Charge (SoC) is defined as the ratio between the available capacity$Q(t)$and the maximum possible amount of charge that can be stored in the battery (nominal capacity)${Q_n}$.
State of Charge $(SoC) = \dfrac{{Q(t)}}{{{Q_n}}}$
We are going to know which is the best instrument used for testing the state of charge (SoC). The answer is Hydrometer and it is the instrument used to test the State of Charge of the battery.
By using Hydrometer, the density of electrolyte is measured by finding the specific gravity of the electrolyte.
In practice,$100\%$the SoC of the aged battery is equal to the $75\%$ to $85\%$ of the new battery. It is mainly caused due to the aging of the battery.
We came to know that the correct answer is option (D) Hydrometer

Note: The hydrometer is commonly used for measuring the SoC of lead-acid Batteries. The percentage can be analyzed by the average specific gravity. If the specific gravity is $1.265$, the SoC of the battery is $100\%$. If the specific gravity is $1.225,1.190,1.120$ , then the Soc of the battery becomes $75\% ,50\% ,0\%$ respectively.
Comparing Hydrometer from the other options given in the question. Voltameter is used to measure the electric charge. The voltmeter is used to measure the electric potential between two points in an electric circuit. The ammeter can be used to measure the current in an electric circuit.