Three equal charges, each having a magnitude of 2.0 x 10^-6 C, are placed at the three corners of a right angled triangle of sides  3 cm,  4 cm  and  5 cm. The force (in magnitude) on the charge at the right angled corner is

• 50 N

• 26 N

• 29 N

• 45.9 N

The rms speed (in m/s) of oxygen molecules of the gas at temperature 300 K, is

• 483

• 504

• 377

• 346

The parts of two concentric circular arcs joined by two radial lines and carries current i. The arcs subtend an angle 0 at the centre of the circle. The magnetic field at the centre O, is

• $\frac{{\mathrm{\mu }}_{0 }\mathrm{i}\left( \mathrm{b} - \mathrm{a} \right) \mathrm{\theta }}{4\mathrm{\pi } \mathrm{ab}}$

• $\frac{{\mathrm{\mu }}_0\mathrm{i} \left(\mathrm{b} - \mathrm{a}\right)}{\left(\mathrm{\pi } - \mathrm{\theta } \right)}$

• $\frac{{\mathrm{\mu }}_0\mathrm{i} \left( \mathrm{b} - \mathrm{a} \right)\mathrm{\theta }}{\mathrm{\pi ab}}$

• $\frac{{\mathrm{\mu }}_0\mathrm{i} \left(\mathrm{a} - \mathrm{b}\right)}{2\mathrm{\pi ab}}$

The ammeter shown in figure consists of a 480 Ω coil connected in parallel to a 20 Ω shunt. The reading of ammeter is

• 0.125 A

• 1.67 A

• 0.13 A

• 0.67 A

An inductor (L = 20 H), a resistor (R = 100 Ω) and a battery (E = 10 V) are connected in series. After a long time, the circuit is short-circuited and then the battery is disconnected. Find the current in the circuit at 1 ms after short circuiting.

• 4.5 x 10⁵ A

• 3.2x 10^-5 A

• 9.8 × 10^-5 A

• 6.7 × 10^-4 A

Two charges of + 10 μC and +20 μC are separated by a distance 2 cm. The net potential (electric) due to the pair at the middle point of the line joining the two changes, is

• 27 MV

• 18 MV

• 20 MV

• 23 MV

47.

A copper rod of length 20 cm and cross-sectional area 2 mm is joined with a similar aluminium rod as shown below

      

The resistance of pair of rods is (ρ_Al =2.6 x 10^-8 Ω-m and  ρ_Cu =1.7 x 10^-8 Ω-m)

• 1.0 mΩ

• 2.0 mΩ

• 3.0 mΩ

• None of these

A square loop is made by a uniform conductor wire as shown in figure

The net magnetic field at the centre of the loop if side length of the square is a

• $\frac{{\mathrm{\mu }}_0 \mathrm{i}}{2 \mathrm{a}}$

• zero

• $\frac{{\mathrm{\mu }}_0 {\mathrm{i}}^2}{{\mathrm{a}}^2}$

• None of these

The electron of H - atom is revolving around the nucleus in circular orbit having radius $\frac{{\mathrm{h}}^2}{4\mathrm{\pi } {\mathrm{me}}^2}$ with $\left(\frac{2\mathrm{\pi } {\mathrm{e}}^2}{\mathrm{h}}\right)$. The current produced due to the motion of electron is

• $\frac{2\mathrm{\pi } {\mathrm{m}}^2 {\mathrm{e}}^2}{3{\mathrm{h}}^2}$

• zero

• $\frac{2 {\mathrm{\pi }}^2 \mathrm{me}}{{\mathrm{h}}^2}$

• $\frac{4{\mathrm{\pi }}^2 {\mathrm{me}}^5}{{\mathrm{h}}^3}$

Two small balls, each carrying a charge q are suspended by equal insulator strings of length l m from the hook of a stand. This arrangement is carried in a satellite in space. The tension in each string will be

• $\frac{1}{4{\mathrm{\pi \epsilon }}_0} \frac{\mathrm{q}}{{\mathrm{l}}^2}$

• $\frac{1}{4{\mathrm{\pi \epsilon }}_0} \frac{{\mathrm{q}}^2}{4{\mathrm{l}}^2}$

• $\frac{1}{4{\mathrm{\pi \epsilon }}_0} \frac{{\mathrm{q}}^2}{{\mathrm{l}}^2}$

• $\frac{1}{\left(4{\mathrm{\pi \epsilon }}_0\right)} \frac{\mathrm{q}}{\mathrm{l}}$