Large transformers, when used for some time, become hot and are cooled by circulating oil. The heating of transformer is due to
|
(a) Heating effect of current alone |
|
(b) Hysteresis loss alone |
|
(c) Both the hysteresis loss and heating effect of current |
|
(d) None of the above |
(c) Both the hysteresis loss and heating effect of current
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A step up transformer connected to a 220 V AC line is to supply 22 kV for a neon sign in secondary circuit. In primary circuit a fuse wire is connected which is to blow when the current in the secondary circuit exceeds 10 mA. The turn ratio of the transformer is
|
(a) 50 |
(b) 100 |
(c) 150 |
(d) 200 |
When NPN transistor is used as an amplifier
|
(a) Electrons move from base to emitter |
|
(b) Electrons move from emitter to base |
|
(c) Electrons moves from base to emitter |
|
(d) Holes moves from base to emitter |
The capacity of a condenser in which a dielectric of dielectric constant 5 has been used, is C. If the dielectric is replaced by another with dielectric constant 20, the capacity will become
|
(a) |
(b) 4C |
(c) |
(d) 2C |
A fuse wire with radius 1 mm blows at 1.5 amp. The radius of the fuse wire of the same material to blow at 3A will be
|
(a) |
(b) |
(c) |
(d) |
A double star is a system of two stars rotating about their centre of mass only under their mutual gravitational attraction. Let the star have mass m and 2m and their separation be l. Their time period of rotation about their centre of mass will be proportional to
|
(a) |
(b) l |
(c) |
(d) |
