Electric Devices

Ohmmeter of internal resistance 3000 Ω its pointer deflects by an angle ( 𝜽 ) when its terminals are connected together and when it is connected with resistance R1 the pointer deflects by an angle ( 𝜽/3 ) and by replacing R₁ by another resistance R₂ the pointer deflects by an angle ( 𝜽/4 ) so the value of R₁ and R₂ equal………..

• (a)

• (b)

• (c)

• (d)

The figure represents a sensitive galvanometer. Which of the following figures correctly represents the modification to the galvanometer to become capable of measuring a maximum current of 1A

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A voltmeter the resistance of its coil is 40 Ω, reaches its full-scale deflection when a current of intensity 0.1A passing through it. Then the value of the multiplier resistance of the device that makes the maximum potential difference reaches 100V between its two ends is …………

• 25 Ω

• 2.5 Ω

• 960 Ω

• 1040 Ω

A galvanometer is connected in series to a resistor of 2000 Ω to convert it into a voltmeter as shown in the figure. So, the maximum voltage can be read by the voltmeter is 20.5 V. If we want to convert the galvanometer into a voltmeter that can read up to 10.25 V, so we need to replace the 2000 Ω resistor by a resistor of …………….

• 1025 Ω

• 1000 Ω

• 975 Ω

• 4000 Ω

In the opposite figure; if the shunt resistance is change so that the sensitivity of the device increases at the same current (I), which of the these ratios increases?Ig

• I_g/I_s

• V_g/V_s

• R_g/R_t

• R_g/R_s

In the ohmmeter circuit; when another external resistance is connected to the unknown resistance (R_x) in series, the pointer stops at 3/5 of the galvanometer scale, then the value of the other external resistance is …………….

• 6R_x

• 5R_x

• 3/2 R_x

• 3R_x

The graph represents the relation between the maximum current intensity measured by an ammeter and the reciprocal of its shunt resistor, so the maximum potential difference between the shunt terminals equals .....

• 0.1 V

• 0.8 V

• 1.2 V

• 1 V

The opposite figure represents the scale of the galvanometer in

the ohmmeter circuit, so the value of R_x, equals ……..

• 6000 Ω

• 10000 Ω

• 12000 Ω

• 18000 Ω

A galvanometer, the resistance of its coil is (R_g), measures a maximum current of (I_g) When a shunt resistance of value R₁ is connected to its coil, its sensitivity gets reduced to 3/4 of its original value. When the shunt is replaced by another of resistance R₂, its sensitivity decreases to 3/8 of its original. So, the ratio :

value of shunt R₁/value of shunt R₂

• 2

• 3

• 4

• 5

A voltmeter, its resistance is 100 Ω and the maximum voltage that can be measured by it is 1 V. The value of multiplier resistance that should be connected to increase the measured

voltage by 10 times equals

• 0.9 kΩ

• 10 kΩ

• 1.1 kΩ

• 1 kΩ