A solid sphere of mass 'M' and radius 'a' is surrounded by a uniform concentric spherical shell of thickness 2a and mass 2M. The gravitational field at distance '3a' from the centre will be :

The pressure wave, P = 0.01 sin [1000t – 3x] Nm^–2, corresponds to the sound produced by a vibrating blade on a day when atmospheric temperature is 0°C. On some other day, when temperature is T, the speed of sound produced by the same blade and at the same frequency is found to be 336 ms^–1 . Approximate value of T is

An NPN transistor is used in common emitter configuration as an amplifier with 1 k$$\Omega $$ load resistance. Signal voltage of 10 mV is applied across the base-emitter. This produces a 3 mA change in the collector current and 15μA change in the base current of the amplifier. The input resistance and voltage gain are :

A moving coil galvanometer has resistance 50$$\Omega $$ and it indicates full deflection at 4mA current. A voltmeter is made using this galvanometer and a 5 k$$\Omega $$ resistance. The maximum voltage, that can be measured using this voltmeter, will be close to :