66. The Wheatstone bridge method of resistance measur ementis idealy suitable for the measurement of resistance values in the range of

1. 1. 0.001 ohm to 1 ohm

   
   
   

   2. 0.1 ohm to 100 ohm

   
   
   

   3. 100 ohm to 10 k-ohm

   
   
   

   4. 100 k-ohm to 10 M-ohm

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: B

   NA

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67. The coils having self-inductance of 10 mH and 15 mH have an effective inductance of 40 mH, when connected in series aiding. What will be t he equivalent inductance if we connect them in series-opposing?

1. 1. 20 mH

   
   
   

   2. 10 mH

   
   
   

   3. 5 mH

   
   
   

   4. zero

   
   
   

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1. View Hint View Answer Discuss in Forum

   L = L₁ + L₂ ± 2M.
   When ordinary, L = L₁ + L₂ + 2M
   ∴ 40 = 10 + 15 + 2M.
   ∴ 2M = 15 mH
   When opposing, L = L₁ + L₂ – 2M
   = 10 + 15 – 15 = 10 mH

   Correct Option: B

   L = L₁ + L₂ ± 2M.
   When ordinary, L = L₁ + L₂ + 2M
   ∴ 40 = 10 + 15 + 2M.
   ∴ 2M = 15 mH
   When opposing, L = L₁ + L₂ – 2M
   = 10 + 15 – 15 = 10 mH

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68. For the ac bridge circuit shown in the figure at balance, the value of R_d, L_d and Q_d will be respectively
    

1. 1. 	Ra	Rb;	RaRc	;ωCbRb
      	Rc		Cb

   
   
   

   2. 	Rb	Rc;	RaRc	;ωCbRb
      	Ra		Cb

   
   
   

   3. 	Rb	Rc;RaRcCb;ωCbRc
      	Ra

   
   
   

   4. 	Ra	Rc;RaRcCb;ωCbRb
      	Rb

   
   
   

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1. View Hint View Answer Discuss in Forum

   From balance condition
   

   RaRc = (RdjωLd	R
   	1 + lωcbRb

   
   or (1 + ω_cbR_b)R_aR_c = R_b(R_d + jωL_d
   or R_bR_d = R_aR_c
   

   ∴ Rd =	RaRc
   	Rb

   
   and ωC_bR_bR_c = ωR_bL_d
   or L_d = R_aR_cC_b

   Correct Option: D

   From balance condition
   

   RaRc = (RdjωLd	R
   	1 + lωcbRb

   
   or (1 + ω_cbR_b)R_aR_c = R_b(R_d + jωL_d
   or R_bR_d = R_aR_c
   

   ∴ Rd =	RaRc
   	Rb

   
   and ωC_bR_bR_c = ωR_bL_d
   or L_d = R_aR_cC_b

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69. The scale of a 0-500 V voltmeter is divided into ten large divisions representing 50 V each and each large division a further subdivided into 10 small divisions, each representing 5 V. It is used for measurement of out put vol t age of a potentiometer which can be varied from 0 to 500 V. It is observed that when the sliding contact moved from its zero position, there is no perceptible movement of pointer of the voltmeter till the sliding contact reaches a position where the output voltage should be 5 V. Therefore, it can be concluded that

1. 1. threshold of the voltmeter is 5 V

   
   
   

   2. resolution of the voltmeter is 5 V

   
   
   

   3. sensitivity of the voltmeter is 5V

   
   
   

   4. none of these

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: A

   NA

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70. A Wheatstone bridge has ratio arms of 1000 W and 100 W resistance, the standard resistance arms consists 4 decade resistance boxes of 1000, 100, 10, 1 W steps. The maximum and minimum values of unknown resistance which can be determined with this set up is

1. 1. 111100 Ω, 1Ω

   
   
   

   2. 111100 Ω, 10 Ω

   
   
   

   3. 111100 Ω, 10 Ω

   
   
   

   4. none of these

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: C

   NA

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