Alternating Cur...

When a sheet of metal is placed in a magnetic field, which changes from zero to a maximum value, the induced current are set up in the direction shown in Fig. what is the direction of magnetic field ?

An aeroplane in which the distance between the tips of the wings is 50 m is flying horizontally with a speed of 360 km/h over a place where the vertical component of earth’s magnetic field is 2×10^-4 Wb/m². The potential difference between the tips of the wings would be

In Fig. final value of current in 10Ω resistor, when plug of key K is inserted is

Fig. represents a primitive motor. A metal wire slides on a horse shoe shaped metal loop of width 0.25m. These have negligible resistance, but there is a 1.0Ω resistor in the circuit as well as a 6.0 V battery. There is uniform magnetic field directed in the plane of the page of magnitude 0.5 T. A force of 0.25 N to the left is required to keep it moving with constant speed to the right, then current flowing is

A motor armature develops a torque of 100 Nm when it draws 40 A from the line. The torque developed if the armature current is increased to 70 A and the magnetic field strength is reduced to 80% of its initial value is

Fig. shows the variation of voltage and current in an a.c. circuit. The circuit contains

An alternating voltage of frequency w is applied in electric circuit consisting of the an inductance L and capacitance C, connected in parallel. Then across the inductance coil,
I. Current is maximum
II. Current is minimum,
III. Voltage is minimum
IV. Voltage is maximum,
Make the correct choice

In a step down transformer, use of 120 V line, provides a pot.diff. of 2400 V. If the primary coil has 75 turns, number of turns in secondary coil is :

The best material for the core of a transformer is

Alternating current cannot be measured by dc ammeter because