A galvanometer has a resistance of 30 Q. It gives full scale deflection with a current of 2mA. Calculate, the value of the resistance needed to convert it into an ammeter of range 0 − 0.3 A. The value of the resistance needed to convert galvanometer into ammeter
0.2 Ω
0.3 Ω
0.4 Ω
0.52 Ω
The given circuit diagram shows a series L-C-R circuit connected to a variable frequency 230 V, source: L =5.0 H, C = 80 µF, R = 40 Ω
The frequency and impedance of the circuit at the resonating frequency are
50 rad/s and 5.75 A
1000 rad/s and 3 A
10 rad/s and 2 A
20 rad/s and 4 A
The instantaneous current and voltage of an AC circuit are given by I= 10 sin 300t A and V = 200 sin 300t V. The power dissipation in the circuit is
500 W
2000 W
1000 W
100 W
In a series L-C-R circuit, the voltages across an inductor, a capacitor and a resistor are 30V, 30V and 60 V respectively. The phase difference between the applied voltage and the current in the circuit is
O°
90°
30°
60°
An AC source, of voltage V =Vm sin ωt, is applied across a series RC circuit in which the capacitive impedance is 'a' times the resistance in the circuit. The value of the power factor of the circuit is
O
None of these
Current in a circuit falls steadily from 2.0 A to 0.0 A in 10 ms. If an average emf of 200 V is induced, then the self-inductance of the circuit is
1 H
2 H
1/2 H
2 H
A rectangular coil of area A, having number of turns N is rotated at f revolutions per second in a uniform magnetic field B. The maximum emf induced in the coil is
fNB
2fNBA
fBA
fNBA
The polarity of the capacitor in the situation described by Fig.
Plate A and plate B both positive
Plate A negative and plate B positive
Plate A positive and plate B negative
Plate A and plate B both negative
C.
Plate A positive and plate B negative
The polarity of plate 'A' will be positive with respect to plate 'B' in the capacitor. Here, the understanding of Lenz's rule is assessed. The polarity nature of two plate will be decided on the basis of direction of flow of induced emf/current which opposes the cause (ie., arrival of magnets). So, north polarity develops when viewed from the left hand side magnet whose north pole is arriving towards loop. North polarity develops when direction of flow of current is anti-clockwise when viewed from the left hand magnets. This make plate A positive and plate B negative.
A step down transformer operated on a 2.5 kV line. It supplies a load with 20 A. The ratio of the primary winding to the secondary is 10 : 1. If the transformer is 90% efficient, the power output is
4.5 X 104 W
4.5 × 102 W
6 x 104 W
6 X 104 w
A step down transformer operated on a 2.5 kV line. It supplies a load with 20 A. The ratio of the primary winding to the secondary is 10 : 1. If the transformer is 90% efficient, the voltage in the secondary is
225 V
550 V
250 V
200 V