Difference Between Ammeter And Voltmeter: Important Questions

The difference between ammeter and voltmeter is that an ammeter measures the current flowing through a circuit while a voltmeter measures the potential difference.

• In an electric circuit, a voltmeter is connected in parallel whereas an ammeter is connected in series.
• The connection polarity of both of these devices is the same.
• The negative terminal is connected with the negative polarity and the positive terminal is connected with the positive polarity of the supply. 

Connection of Voltmeter and Ammeter in a Circuit

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Very Short Answer Questions (1 Mark Questions)

Ques. What is an ammeter?

Ans. An ammeter is a device used to measure the value of current flowing in a circuit. It is always connected in series with the circuit. 

Ques. What is a voltmeter? 

Ans. A voltmeter is a device that is connected in parallel with a circuit and measures the potential difference applied across two ends of the circuit. 

Ques. What is a differential voltmeter?

Ans. The differential voltmeter is one that is used to measure the voltage difference between a known and an unknown source. It is also called a ‘Potentiometer Voltmeter’ since its working principle is similar to that of the potentiometer. 

Ques. How can a galvanometer be converted into an ammeter?

Ans. To convert a galvanometer into an ammeter, a low resistance called a ‘shunt’ is connected in parallel to the galvanometer. This reduces the resistance offered by the galvanometer and thus the current flowing through it can be measured. 

Ques. A current of 300 mA is made to flow through a 6 kΩ resistor. What is the potential difference across the resistor?

Ans. According to Ohm’s law, V = IR

I = 300 mA = 0.3 A and R = 6 kΩ = 6000 Ω

So, V = 0.3 x 6000 = 1800 V

Ques. Define current electricity.

Ans. The flow of charged particles such as electrons and ions from one part of the circuit to another part is called current electricity.

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Short Answer Questions (2 Marks Questions)

Ques. What are the different types of voltmeters?

Ans. Depending upon their construction, voltmeters are of the following types:

1. Permanent Magnet Moving Coil Voltmeter
2. Moving Iron Voltmeter
3. Electro Dynamometer Type Voltmeter
4. Rectifier Type Voltmeter
5. Induction Type Voltmeter
6. Electrostatic Type Voltmeter
7. Digital Voltmeter

Ques. Name the different types of ammeter.

Ans. Based on their construction, the different types of ammeters are:

1. Permanent Moving Coil Ammeter
2. Moving Iron Ammeter
3. Electro-dynamometer ammeter
4. Rectifier-type Ammeter

Ques. What is the difference between DC Voltmeter and AC Voltmeter?

Ans. The DC voltmeter measures the DC voltage while the AC voltmeter measures the AC voltage. In a DC voltmeter, the peak value of DC voltage is measured whereas an AC voltmeter measures the RMS value of AC voltage. 

Ques. What will happen if a voltmeter is connected in series with a circuit?

Ans. The resistance of a voltmeter is very high. If it is connected in series with the circuit, then it will draw a large amount of current from it and will not give accurate readings of voltage. That is why a voltmeter is always connected in parallel so that it allows the flow of the current through the circuit. The resistance of an ideal voltmeter is infinite to ensure that the current drawn by it is negligible. 

Ques. What will happen if an ammeter is connected in parallel with a circuit?

Ans. An ammeter is always connected in series with the circuit because:

1. It offers very low resistance to the current, thus it measures the accurate value of the current by allowing it to pass through it completely.
2. If it is connected in parallel, it might cause a short circuit and damage the device.

Ques. Two resistors of resistance 3 Ω each are connected in series with a 12 V battery. Find the current flowing through each resistor.

Ans. Since the two resistors are connected in series, therefore equivalent resistance of the circuit is

R_eq = R₁ + R₂ = 3 + 3 = 6 Ω

Using Ohm’s law, V = IR, we have

Current flowing through the circuit, I = V/R

⇒ I = 12/6 = 2A

Hence, current of 2 A is flowing through each resistor.

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Long Answer Questions (3 Marks Questions)

Ques. What are the readings of the voltmeter and ammeter in the following circuit?

Ans. In the above diagram, the net resistance of the resistors connected in parallel is,

1/R_P = 1/100 + 1/100 

1/R_P = 2/100 = 1/50

R_P = 50

This is connected in series with another resistor of 100, therefore the net resistance is:

R_eq = 100 + 50 

R_eq = 150

I = V/R

I = 6/150

I = 0.04 A   (Reading of Ammeter)

Now, V = IR

V = 0.04 100 

V = 4 V      (Reading of Voltmeter)

Ques. Find the reading of the voltmeter in the circuit given below.

Ans. In the circuit shown above, the net resistance is,

Req = 300  

I = V / R_eq  

I = 30 / 300 = 0.1 A

Now, reading of voltmeter (V) = IR

V = 0.1 125 

V = 12.5 V

Ques. What is the reading of the ammeter in the circuit given below?

Ans. In the above circuit, the effective resistance is,

R_eff = 10 + 20/3 + 5

R_eff = 65/3

I = V/R_eff 

I = (5 3) / 65 

I = 3/13 A

Ques. What are the key differences between an ammeter and a voltmeter?

Ans. The key differences between an ammeter and a voltmeter are tabulated below:

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Very Long Answer Questions (5 Marks Questions)

Ques. In the circuit, R₁ = 400 and R₂ = 200. If the resistance of the voltmeter is 10,000, then find the reading of the voltmeter. 

Ans. Here, the equivalent resistance is,

R_eq = 400 + (200 10000) / (200 + 10000)

R_eq = 400 + 196 = 596

I = V/R = 6/596 A

The potential across R₁ is given by, 

V₁ = IR₁ 

V₁ = 6/596 400 

V₁ = 4.026 V

The potential across R₂ is given by,

V₂ = 6 - 4.026 

V₂ = 1.974 V

Hence, the reading of the voltmeter = 1.97 V

Ques. In the circuit given below, the variable resistor X is adjusted so that high resistance voltmeter V shows a reading of 1 V. Find the resistance. 

Ans. In the upper part (through 5V voltage),

V_A + 2i - 5 = V_B     (i = current through the circuit)

Now, V_A - V_B = 5 - 2i = 1

i = (5 - 1) / 2 

i = 2 A

In the lower part (through 2V voltage),

V_A + 2 - iX = V_B 

iX = V_A - V_B + 2

But, V_A - V_B = 1 V, and i = 2 A

So, X = (1 + 2) / 2 

X = 1.5

Ques. Find the reading of the ammeter in the circuit given below.

Ans. The distribution of current in the circuit is as follows:

Here, I₁ = 4.5/9 = 0.5 A

The resistors (9, 3) and 6 are in parallel, so

4.5 + 3I₁ = 6I2 

4.5 + 3(0.5) = 6I2 

I₂ = (4.5 + 1.5) / 6 

I₂ = 1 A

I = I₁ + I₂ = 0.5 + 1 = 1.5 A

Equivalent resistance between C and D (R_CD) = (1/10 + 1/12 + 1/15)-1 = 4

Potential across C and D (V_CD) = IR_CD = 1.5 4 = 6V

The potential across A and D is,

V_AD = V_AB + V_BC + V_CD 

V_AD = 6I₂ + 2I + 6 

V_AD = 6(1) + 2(1.5) + 6 

V_AD = 6 + 3 + 6 = 15 V

Since 20 is connected in parallel across total resistance across A and D, so this will be the potential across 20 as well as the voltmeter. 

Thus, I₄ = 15/20 = 0.75 A

Reading in the ammeter = I + I₄ = 1.5 + 0.75 = 2.25 A

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