A long wire carrying a steady current is bent into a circular loop of one turn. The magnetic field at the centre of the loop is B. It is then bent into a circular coil of n turns. The magnetic field at the centre of this coil of n turns will be :

A filament bulb (500 W, 100 V) is to be used in a 230 V main suply. When a resistance R is connected in series, it works perfectly and the bulb consumes 500 W. The value of R is : 

The potential difference (V_A – V_B) between the points A and B in the given figure is :

A parallel- plate capacitor of area A, plate separation d and capacitance C is filled with four dielectric materials having dielectric constant k₁, k₂, k₃ and k₄ as shown in the figure below. If a single dielectric material is to be used to have the same capacitance C in this capacitor, then its dielectric constant k is given by

An electric dipole is placed at an angle of 30º with an electric field intensity 2 ×10⁵ N/C. It experiences a torque equal to 4 N m. The charge on the dipole, if the dipole length is 2cm, is

Three sound waves of equal amplitudes have frequencies (n –1), n, (n + 1). They superimpose to give beats. The number of beats produced per second will be