A potentiometer has uniform potential gradient. The specific resistance of the material of the potentiometer wire is 10-7 ohm-metre and the current passing through it is 0.1 ampere, cross-section of the wire is 10-6 m2. The potential gradient along the potentiometer wire is
10-6 V/m
10-4 V/m
10-8 V/m
10-2 V/m
A fuse wire with radius 1 mm blows at 1.5 ampere. The radius of the fuse wire of the same material to blow at 3A will be
31/4 mm
41/3 mm
31/2 mm
21/3 mm
B.
41/3 mm
The temperature of the wire increase to such a value at which the heat produced per second equals heat lost per second due to radiation.
where H is heat lost per second per unit area due to radiation.
A wire in the form of a circular loop of one turn carrying a current produces a magnetic field B at the centre. If the same wire is looped into a coil of two turns and carries the same current, the new value of magnetic induction at the centre is
3B
5B
4B
2B
To send 10% of the main current through a moving coil galvanometer of resistance 99 ohm, the shunt required is
10 ohm
9.9 ohm
9 ohm
11 ohm
The magnetic flux linked with a coil at any instant 't' is given by the emf induced in the coil at t = 2 second is
40 V
− 40 V
300 V
140 V
A charged particles moves along the line AB which lies in the same plane of a circular loop of conducting wire as shown in the figure. Then
no current will be induced in the loop
the current induced in the loop will change its direction as the charged particle passes by
the current induced will be anti-clockwise
the current induced will be clockwise
The time taken by AC of 50 Hz in reaching from zero to the maximum value is
50 × 10-3 sec
5 × 10-3 sec
1 × 10-3 sec
2 × 10-3 sec
The ratio of the secondary to the primary turns in a transformer is 3 : 2 and the output power is P. Neglecting all power losses, the input power must be
P
The material used for permanent magnet has
low retentivity, high coercivity
high retentivity, low coercivity
high retentivity, high coercivity
low retentivity, low coercivity
A fish, looking up through the water sees the outside world contained in a circular horizon. If the refractive index of water is 4/3 and the fish is 12 cm below the surface of water, the radius of the circle in centimetre is