6. In the two-wattmeter method of measuring power in a balanced three-phase circuit, one wattmeter shows zero and the other positive maximum. The load power factor is _________

1. 1. 0.5

   
   
   

   2. 0.2

   
   
   

   3. 1.2

   
   
   

   4. 1.5

   
   
   

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1. View Hint View Answer Discuss in Forum

   The wattmeters reading is proportional to cos (30 + φ)
   Then other is proportional cos (30 – φ)
   Thus whenever load p.f. angle φ becomes 60°, one of the wattmeters would read zero.
   Hence for the given condition load load
   p.ƒ = cos 60° = 0.5

   Correct Option: A

   The wattmeters reading is proportional to cos (30 + φ)
   Then other is proportional cos (30 – φ)
   Thus whenever load p.f. angle φ becomes 60°, one of the wattmeters would read zero.
   Hence for the given condition load load
   p.ƒ = cos 60° = 0.5

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7. The internal resistance of a Weston standard cell is of the order of ___________Ω

1. 1. 2

   
   
   

   2. 3

   
   
   

   3. 1

   
   
   

   4. 5

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: C

   NA

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8. A 35 V dc supply is connected across a resistance of 600 ohm in series with an unknown resistance R_x. A voltmeter having a resistance of 1.2 k-ohm is connected across 600 ohm resistance and reads 5V. The value of resistance R_x will be _________kΩ

1. 1. 2.4

   
   
   

   2. 2.1

   
   
   

   3. 2.5

   
   
   

   4. 2.9

   
   
   

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1. View Hint View Answer Discuss in Forum

   Voltage across R₁, V₁ = 35 – 5 = 30V
   
   

   Current in the circuit, I =	E		=	1	A
   	600 × 1200			400
   	600 + 1200

   
   

   ∴ Rx =	30 × 400	= 2.4 kΩ
   	5

   Correct Option: A

   Voltage across R₁, V₁ = 35 – 5 = 30V
   
   

   Current in the circuit, I =	E		=	1	A
   	600 × 1200			400
   	600 + 1200

   
   

   ∴ Rx =	30 × 400	= 2.4 kΩ
   	5

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9. A permanent magnet moving coil type ammeter and a moving iron type ammeter are connected in series in a resistive circuit fed from output of a half wave rectifier voltage source. If the moving iron type instrument reach 5 A, the permanent magnet moving coil type instrument is likely to read __________A

1. 1. 3.18

   
   
   

   2. 3

   
   
   

   3. 25

   
   
   

   4. 5

   
   
   

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1. View Hint View Answer Discuss in Forum

   For half wave rectifier output,
   

   Idc =	Im	and Irms =	Im
   	π		2

   
   Hence PMMC reading will be,
   

   Idc =	2 × 5	= 3.18 amp
   	π

   Correct Option: A

   For half wave rectifier output,
   

   Idc =	Im	and Irms =	Im
   	π		2

   
   Hence PMMC reading will be,
   

   Idc =	2 × 5	= 3.18 amp
   	π

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10. A galvanometer is tested shown in figure, in the circuit, where E = 1.5 V, R₁ = 1.0 ohm, R₂ = 2500 ohm and R₃ is variable. With R₃ set at 450 ohm, the galvanometer deflection is 140 mm and with R₃ set at 950 ohm, the galvanometer deflection is 70 mm. The resistance of t he galvanometer is ___________
    

1. 1. 55

   
   
   

   2. 25

   
   
   

   3. 49

   
   
   

   4. 59

   
   
   

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1. View Hint View Answer Discuss in Forum

   It is simple resistive circuit calculation.
   

   Ic =	1	E
   	1 + R3 + RG	2500 +	1(R3 + RG)
   			1(R3 + RG)

   
   From the given data,
   

   	1	1
   	1 + 450 + RG	2500 +	1(450 + RG)
   			1(450 + RG)

   
   

   =	1	1
   	1 + 450 + RG	2500 +	950 + RG
   			1 + 950 + RG

   
   or 2500 (451 + R_G) + 450 + R_G = 2500 (951+ R_G) + 50
   or 2501 R_G = 2500 (951 – 902) + 50
   or R_G = 49 ohms.

   Correct Option: C

   It is simple resistive circuit calculation.
   

   Ic =	1	E
   	1 + R3 + RG	2500 +	1(R3 + RG)
   			1(R3 + RG)

   
   From the given data,
   

   	1	1
   	1 + 450 + RG	2500 +	1(450 + RG)
   			1(450 + RG)

   
   

   =	1	1
   	1 + 450 + RG	2500 +	950 + RG
   			1 + 950 + RG

   
   or 2500 (451 + R_G) + 450 + R_G = 2500 (951+ R_G) + 50
   or 2501 R_G = 2500 (951 – 902) + 50
   or R_G = 49 ohms.

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