21.

A battery of emf 10 V and internal resistance 3 Ω is connected to a resistor. The current in the circuit is 0.5 A. The terminal voltage of the battery when the circuit is closed is

• 10 V

• 0 V

• 1.5 V

• 8.5 V

A galvanometer coil has a resistance of 15 Ω and gives full scale deflection for a current of 4 mA. To convertit to an ammeter of range 0 to 6 A

• 10 m Ω resistance is to be connected in parallel to the galvanometer

• 10 m Ω resistance is to be connected in series with the galvanometer

• 0.1 Ω resistance is to be connected in parallel to the galvanometer

• 0.1 Ω resistance is to be connected in series with the galvanometer

The electron dirft speed is small and the charge of the electron is also small but still, we obtain large current in a conductor. This is due to

• the conducting property of the conductor

• the resistance of the conductor is small

• the electron number density of the conductor is small

• the electron number density of the conductor is enormous

A straight wire of mass 200 g and length 1.5 m carries a current of 2 A. It is suspended in mid-air by a uniform horizontal magnetic field B. The magnitude of B (in tesla) is (assume g = 9.8 ms^-2)

• 2

• 1.5

• 0.55

• 0.65

In the circuit shown, the value of I in ampere is

• 1

• 0.60

• 0.4

• 1.5

A Gaussian sphere encloses an electric dipole within it. The total flux across the sphere is

• zero

• half that due to a single charge

• double that due to a single charge

• dependent on the position of the dipole

A parallel plate air capacitor has a capacitance C. When it is half filled with a dielectric of dielectric constant 5, the percentage increase in the capacitance will be 

• 400 %

• 66.6 %

• 33.3 %

• 200 %

A comb run through one's dry hair attracts small bits of paper. This is due to

• comb is a good conductor

• paper is a good conductor

• the atoms in the paper get polarised by the charged comb

• the comb possesses magnetic properties

The top of the atmosphere is about 400 kV with respect to the surface of the earth, corresponding to an electric field that decreases with altitude. Near the surface of the earth, the field is about 100 Vm^-1. Still, we do not get an electric shock as we step out of our house into the open house because (assume the house to be a steel cage so that there is no field inside)

• there is a potential difference between our body and the ground

• 100 Vm^-1 is not a high electric field so that we do not feel the shock

• our body and the ground forms an equipotential surface

• the dry atmosphere is not a conductor

The specific charge of a proton is 9.6 × 10⁷ C kg^-1. The specific charge of an alpha particle will be

• 9.6 × 10⁷ C kg^-1

• 19.2 × 10⁷ C kg^-1

• 4.8 × 10⁷ C kg^-1

• 2.4 × 10⁷ C kg^-1