Ammeter

Q. In an ammeter, $0.2\%$ of main current passes through the galvanometer. If resistance of galvanometer is $G$, then the resistance of ammeter will be -

1. $\frac{499}{500}G$
   
2. $\frac{1}{499}G$
3. $\frac{1}{500}G$
4. $\frac{500}{499}G$

Q.

Define the current sensitivity of the galvanometer. Write its SI unit.

Q. If each resistance in the figure is of $9\Omega$ then reading of ammeter is

1. 5 A
2. 2 A
3. 8 A
4. 9 A

Q.

What is CT and PT ratio in transformer?

Q. Two cells of same emf $E$ but internal resistance $r_1$ and $r_2$ are connected in series to an external resistor $R$ (figure). What should be the value of $R$ so that the potential difference across the terminals of the first cell becomes zero.

Q. 20. In a circuit diagram shown below what is the reading of ideal ammeter (A)?

Q.

There are two coils $A$ and $B$ as shown in figure. $A$ current start flowing in $B$ as shown when $A$ is moved towards $B$ and stops when $A$ stops moving. The current in $B$ is counterclockwise. $B$ is kept stationary when $A$ moves. We can infer that

1. There is a constant current in the clockwise direction in A

2. There is no current in A

3. There is a varying current in A

4. There is a constant current in the counterclockwise direction in A

Q. A galvanometer having 30 divisions has a current sensitivity of $20\mu A/div$.It has a resistance of 25 ohm. How will you convert it into an ammeter measuring upto 1 ampere. Find shunt to be used

1. $0.15\Omega$
2. $0.015\Omega$
3. $0.030\Omega$
4. $0.30\Omega$

Q. Equivalent resistance between the points $A$ and $B$ is (in $\Omega$)

1. $\frac{1}{5}$
2. $\frac{5}{4}$
3. $\frac{7}{3}$
4. $\frac{7}{2}$

Q. One of the two identical conducting wires of length $L$ is bent in the form of a circular loop and the other one into a circular coil of $N$ identical turns. If the same current is passed in both, The ratio of the magnetic field at the centre of the loop $\left(B_L\right)$ to that at the centre of the coil $\left(B_C\right)$, i.e. $\frac{\left(B_L\right)}{\left(B_C\right)}$ will be

1. $N^2$
2. $N$
3. $\frac{1}{N}$
4. $\frac{1}{N^2}$

Q. An ammeter is obtained by shunting a $30\Omega$ galvanometer with a $30\Omega$ resistance. What additional shunt should be connected across it to double its range?

1. $30\Omega$
2. $15\Omega$
3. $10\Omega$
4. $5\Omega$

Q. The resistance of 1 A ammeter is $0.018\Omega$. To convert it into 10 A ammeter, the shunt resistance required will be

1. $0.18\Omega$
2. $0.12\Omega$
3. $0.0018\Omega$
4. $0.002\Omega$

Q. Explain, using a labelled diagram, the principle and working of a moving coil galvanometer. What is the function of (i) uniform radial magnetic field, (ii) soft iron core ? Define the terms (i) current sensitivity and (ii) voltage sensitivity of a galvanometer. Why does increasing the current sensitivity not necessarily increase voltage sensitivity ?

Q.

Is a potentiometer analog or digital?

Q. A milliammeter of range 10 mA has a coil of resistance $1\Omega$. To use it as voltmeter of range 10 volt, the resistance that must be connected in series with it will be

1. $99\Omega$
2. $1000\Omega$
3. $999\Omega$
4. $100\Omega$

Q. A parallel plate capacitor is to be designed with a voltage rating $1kV$, using a material of dielectric constant $3$ and dielectric strength about ${10}^{7}V/m$. (Dielectric strength is the maximum electric field a material can tolerate without breakdown, i.e., without starting to conduct electricity through partial ionization.) For safety, we should like the field never to exceed, say $10\%$ of the dielectric strength. What minimum area of the plates is required to have a capacitance of $50pF$?

Q.

How to turn a galvanometer to ammeter

Q.

Why Carey Fosters bridge is so sensitive ?

Q.

If the voltage supply to an appliance is reduced to half of its voltage rating, what would be the effect on the power consumed by it?

Q. A magnetic field of $100G(1G={10}^{-4}T)$ is required which is uniform in a region of linear dimension about $10cm$ and area of cross-section about ${10}^{-3}{m}^2$. The maximum current-carrying capacity of a given coil of wire is $15A$ and the number of turns per unit lenght that can be wound round a core is at most $1000\text{turns per meter}$. Suggest some apporiate design particulars of a solenoid for the required purpose. Assume the core is not ferromagnetic.

Q.

The coil $A$ is made to rotate about a vertical axis as shown in figure. No current flows in $B$ if A is at rest. The current in coil $A,$ when the current in $B$ $(att=0)$ is counterclockwise and the coil $A$ is as shown at this instant, $t=0,$ is

1. constant current counterclockwise

2. constant current clockwise

3. varying current counterclockwise

4. varying current clockwise

Q. Why we use rheostat in Meter bridge?

Q.

Figure (32.E2) shows an arrangement to measure the emf $ϵ$ and internal resistance r of a battery. The voltmeter has a very high resistance and the ammeter also has some resistance. The voltmeter reads 1.52 V when the switch S is open. When the switch is closed the voltmeter reading drops to 1.45 V and the ammeter reads 1.0 A. Find the emf and the internal resistance of the battery.

Figure (32.E2)

Q.

What is the symbol of the galvanometer?

Q. A galvanometer of resistance $25\Omega$ gives full scale deflection at 10mA current. It is used as Ammeter with two terminals A and B as shown in figure. One of the terminals (i.e either A or B) is used at a time. Find ratio of range of Ammeter when used between terminal A to terminal B. i.e Find $\frac{I_A}{I_B}.$

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

Q. Draw the circuit symbols for p-n-p and n-p-n transistors.

Q. A $1\Omega$ resistance is in series with an ammeter which is balanced by 75 cm of potentiometer wire. A standard cell of 1.02 V is balanced by 50 cm. The ammeter shows a reading of 1.5A. The error in the ammeter reading

1. 0.002 A
2. 0.03 A
3. 1.01 A
4. no error

Q. When a forward bias is applied to a p−n junction, it
A) raises the potential barrier.
B) reduces the majority carrier current to zero.
C) lowers the potential barrier.
D) None of the above.

Q. Because of the shunt, the ammeter’s overall resistance is

1. Average
2. Medium
3. Large
4. Very small

Q. A battery $E_A$ of $123V$ emf and internal resistance $0.4\Omega$ and a battery $E_B$ of $117V$ emf and internal resistance $0.6\Omega$ supplies a current to load resistance $R_L$ through four wires of resistors $R_A=1.2\Omega ,R_B=1\Omega ,R_C=1.4\Omega$ and $R_D=1.4\Omega$ as shown in figure. The value of load resistance for maximum load power is

1. $1.5\Omega$
2. $3\Omega$
3. $6\Omega$
4. $4.5\Omega$