Galvanometer

Q.

Current sensitivity of a moving coil galvanometer is $\frac{5div}{A}$ and its voltage sensitivity (angular deflection per unit voltage applied) is $20{\times 10}^{-3}divvol{t}^{-1}$ The resistance of the galvanometer is

1. 250Ω
2. 25Ω
3. 40Ω
4. 500Ω

Q.

A galvanometer of resistance $G$ is converted into a voltmeter of range $0–1V$ by connecting a resistance $R_1$ in series with it. The additional resistance that should be connected in series with $R_1$ to increase the range of the voltmeter to$0–2V$ will be:

1. $G$

2. $R_1-G$

3. $R_1+G$

4. $R_1$

Q.

What is the zero error of voltmeter and ammeter?

Q. The sensitivity of a moving coil galvanometer can be increased by

1. Increasing the number of turns in the coil
2. Decreasing the area of the coil
3. Increasing the current in the coil
4. Introducing a soft iron core inside the coil

Q. An unknown resistance $R_1$ is connected in series with a resistance of $10\Omega$ . This combination is connected in one gap of a meter bridge, while a resistance $R_2$ is connected in the other gap. The balance point is obtained at $50\text{cm}$ mark. When the $10\Omega$ resistance is removed, the balance point shifts to $40\text{cm}$ mark. The value of $R_1$ is -

1. $20\Omega$
2. $30\Omega$
3. $10\Omega$
4. $40\Omega$

Q. A galvanometer having a resistance of $8\Omega$ is shunted by a wire of resistance $2\Omega$. If the total current is 1 ampere, the part of it passing through the shunt will be

1. 0.25 amp
2. 0.8 amp
3. 0.2 amp
4. 0.5 amp

Q.

(a) In a metre bridge [Fig. 3.27], the balance point is found to be at 39.5 cm from the end A, when the resistor Y is of 12.5 Ω. Determine the resistance of X. Why are the connections between resistors in a Wheatstone or meter bridge made of thick copper strips?

(b) Determine the balance point of the bridge above if X and Y are interchanged.

(c) What happens if the galvanometer and cell are interchanged at the balance point of the bridge? Would the galvanometer show any current?

Q.

Define wheatstone bridge.

Q. A moving coil galvanometer is converted into an ammeter reading upto 0.03 A by connecting a shunt of resistance 4r across it and into an ammeter reading upto 0.06 A when a shunt of resistance r connected across it. What is the maximum current which can be sent through this galvanometer if no shunt is used.

1. 0.01 A
2. 0.02 A
3. 0.03 A
4. 0.04 A

Q.

What are the advantages of digital voltmeter?

Q.

State the principle of moving coil galvanometer.

Q. A moving coil galvanometer of resistance $20\Omega$ gives a full scale deflection when a current of $1\text{mA}$ is passed through it. It is to be converted into an ammeter reading $20\text{A}$ on full scale. But the shunt of $0.005\Omega$ only is available. What resistance should be connnected in series with the galvanometer coil?

1. $39.995\Omega$
2. $60.995\Omega$
3. $79.995\Omega$
4. $80.995\Omega$

Q.

Name three liquids, which when tested in the manner shown in Fig., may cause the magnetic needle to deflect.

Q. If an ammeter is to be used in place of a voltmeter, then we must connect with an ammeter a

1. low resistance in parallel
2. high resistance in parallel
3. high resistance in series
4. low resistance in series

Q.

Explain the phenomenon of electromagnetic induction. Describe an experiment to show that a current is set up in a closed loop when an external magnetic field passing through the loop increases or decreases.

Q. In a potentiometer arrangement for determining the emf of a cell, the balance point of the cell in open circuit is 350 cm. When a resistance of 9 $\Omega$ is used in the external circuit of the cell, the balance point shifts to 300 cm. Determine the internal resistance of the cell.

Q.

A circular coil of radius $R$ and $N$ turns has negligible resistance. As shown in the schematic figure, its two ends are connected to two wires and it is hanging by those wires with its plane being vertical. The wires are connected to a capacitor with charge$Q$ through a switch. The coil is in a horizontal uniform magnetic field $B_0$ parallel to the plane of the coil. When the switch is closed, the capacitor gets discharged through the coil in a very short time. By the time the capacitor is discharged fully, magnitude of the angular momentum gained by the coil will be (assume that the discharge time is so short that the coil has hardly rotated during this time)

1. $\frac{\pi }{2}NQ{B}_0{R}^2$

2. $\pi NQ{B}_0{R}^2$

3. $2\pi NQ{B}_0{R}^2$

4. $4\pi NQ{B}_0{R}^2$

Q. Which one has resistance - ammeter or Mili ammeter?why?

Q. Two tangent galvanometers $\text{A}$ and $\text{B}$ have coils of radii $8\text{cm}$ and $16\text{cm}$ respectively and resistances $8\Omega$ each. They are connected in parallel with a cell of $\text{emf}4\text{V}$ and negligible internal resistance. The deflections produced in the tangent galvanometer $\text{A}$ and $\text{B}$ are ${30}^{\circ }$ and ${60}^{\circ }$ respectively. If $\text{A}$ has two turns then $\text{B}$ must have .

Q. A circular coil with area $A$ and $N$ turns is free to rotate about a diameter that coincides with the $x-$ axis . Current $I$ is circulating in the coil. There is a uniform magnetic field $\overrightarrow{B}$ on the positive $y-$ direction. Calculate the magnitude and direction of the torque $\overrightarrow{\tau }$.

1. $NIAB;\hat{j}$
2. $NIAB;-\hat{j}$
3. Zero
4. $NIAB;\hat{i}$

Q. In the electric network shown, when no current flows through the $4\Omega$ resistor in the arm EB, the potential difference between the points A and D will be:

1. 3 V
2. 5 V
3. 4 V
4. 6 V

Q.

What would you suggest to a student if while performing an experiment he finds that the pointer/needle of the ammeter and voltmeter do not coincide with the zero marks on the scales when the circuit is open? No extra ammeter/voltmeter is available in the laboratory.

Q. A galvanometer shows a reading of $0.65\text{mA}$. When a galvanometer is shunted with a $4\Omega$ resistance, the deflection is reduced to $0.13\text{mA}$. If the galvanometer is further shunted with a $2\Omega$ wire, the new reading will be (the main current remains the same)

1. $0.60\text{mA}$
2. $0.08\text{mA}$
3. $0.12\text{mA}$
4. $0.05\text{mA}$

Q. A circular ring of radius r made of non conducting material is placed with its axis parallel to a uniform electric field. The ring is rotated about a diameter through 180 degrees. Does the flux of electric field change? If yes, does it increase or decrease?

Q. A moving coil galvanometer of resistance $100\Omega$ is used as an ammeter using a resistance $0.1\Omega$. The maximum deflection current in the galvanometer is $100\mu \text{A}$. Find the minimum current in the circuit, so that the ammeter shows maximum deflection

1. $100.1\text{mA}$
2. $1000.1\text{mA}$
3. $10.01\text{mA}$
4. $1.01\text{mA}$

Q. The magnetic field inside a toroid of radius $R$ is $B$. If the current through it is doubled and the radius increased four times keeping the number of turns per unit length same, then the magnetic field produced by it will be

1. $B$
2. $2B$
3. $4B$
4. $\frac{B}{2}$

Q. A meter bridge setup is shown in the figure. It is used to determine an unknown resistance $R$ using a given resistor of $15\Omega$. The galvanometer $\left(G\right)$ shows null deflection when tapping key is at $43cm$ mark from end $A$. If the end correction for end $A$ is $2cm$, then the determined value of $R$ will be $\Omega$

Q. As shown in the figure, three sided frame is pivoted at $\text{P}$ and $\text{Q}$ and hangs vertically. Its sides are of same length and have a linear mass density of $\sqrt{3}{\text{kgm}}^{-1}$. A current of $10\sqrt{3}\text{A}$ is sent through the frame, which is placed in a uniform magnetic field of $2T$ directed upwards as shown. Then the angle (in degree) through which the frame will be deflected in equilibrium is (Take $g=10{\text{ms}}^{-2}$)

Q. A.C ammeter & voltmeter reads ______of alternating current and voltage.

1. maximum value
2. root mean square value
3. mean square value
4. average value

Q. The magnetic needle of a tangent galvanometer is deflected at an angle ${30}^o$ due to a magnet. The horizontal component of earth's magnetic field $0.34\times {10}^{-4}T$ is along the plane of the coil. The magnetic intensity (of coil) is

1. $1.96\times {10}^{-4}T$
2. $1.96\times {10}^{5}T$
3. $1.96\times {10}^{-5}T$
4. $1.96\times {10}^{4}T$