21.

When plate voltage in diode valve is increased from 100V to 150V. Then, plate increases from 7.5 mA to 12 mA, then dynamic plate resistance will be

• 10 kΩ

• 11 kΩ

• 15 kΩ

• 11.1 kΩ

A charged particle is accelerated by a potential of 200 V. If its velocity is 8.4 × 10⁸ m/s, then value  of e/m for that particle is

• 17.6 × 10¹⁶

• 14.5 × 10¹²

• 1.76 × 10¹⁵

• 1.45 × 10¹⁵

Two capacitors of capacities C₁ and C₂ are charged upto the potential V₁ and V₂ then condition for not flowing the charge between on connected them in parallel is

• C₁ = C₂

• C₁V₁ = C₂V₂

• V₁ =V₂

• $\frac{{\mathrm{C}}_1}{{\mathrm{V}}_2} =\frac{{\mathrm{C}}_2}{{\mathrm{V}}_2}$

Find equivalent resistance between X and Y

• R

• R/L

• 2R

• 5R

If we change the value of R, then

• voltage does not change on L

• voltage does not change on LC combination

• voltage does not change on C

• voltage changes on LC combination

If V =ary, then electric field at a point will be proportional to

• r

• r ^-1

• r ^-2

• r²

Electric field at point 20 cm away from the centre of dielectric sphere is 100 V/m, radius of sphere is 10 cm, then the value of electric field at a distance 3 cm from the centre is

• 100 V/m

• 125 V/m

• 120 V/m

• 0

Real power consumption in a circuit is least when it contains.

• high R, low L

• high R, high L

• low R, high L

• high R, low C

Magnetic field at point O will be

• $\frac{{\mathrm{\mu }}_{\mathrm{o}} \mathrm{I}}{2\mathrm{R}}$ interior

• $\frac{{\mathrm{\mu }}_{\mathrm{o}}\mathrm{I}}{2\mathrm{R}}$ exterior

• $\frac{{\mathrm{\mu }}_{\mathrm{o}} \mathrm{I}}{2\mathrm{R}}\left(1 - \frac{\mathrm{l}}{\mathrm{\pi }}\right)$ interior

• $\frac{{\mathrm{\mu }}_{\mathrm{o}}\mathrm{I}}{2\mathrm{R}} \left(1 + \frac{\mathrm{I}}{\mathrm{\pi }}\right)$ exterior

Magnetic field of the earth is H =0.3 g. A magnet is vibrating 5 oscillations per min then the dippreciation required in the magnetic field of the earth of increase time period upto 10 oscillations per minute is

• 2.25 g

• 0.6 g

• 0.9 g

• 0.12 g