Why can't we see air ?

The drift speed is defined as v_(d)=(Delta l//Delta t) where (Delta l)is the distance drifted in a long time (Delta t). Why don't we define the drift speed as the limit of (Delta l//Delta t) as (Delta t (rarr)0)?

A current i_(0) is flowing through an L-R circuit of time constant t_(0) . The source of the current is switched off at time t = 0 . Let r be the value of (-di//dt) at time t = 0 .Assuming this rate to be constant, the current will reduce to zero in a time interval of

Consider the circuit shown below. When switch S_(1) is closed, let I be the current at time t, then applying Kirchhoff's law E-iR-L (di)/(dt) = 0 or int_(0)^(i) (di)/(E-iR) = 1/L int_(0)^(1) dt i=E/R (1-e^(-R/l *t)) L/R = time constant of circuit When current reaches its steady value (=i_(0) , open S_(1) and close S_(2) , the current does reach to zero finally but decays expnentially. The decay equation is given as i=i_(0)e^(-R/L *T) ). When a coil carrying a steady current is short circuited, the current decreases in it eta times in time t_(0) . The time constant of the circuit is

In Fig. there is a conducting loop ABCDEF of resistance lambda per unit length placed near a long straight current-carrying wire. The dimension are shows in the figure. The long wire lies in the plane of the loop. The current in the long wire varies as I = I_(0)(t) . The heat produced in the loop in time t is

In Fig. there is a conducting loop ABCDEF of resistance lambda per unit length placed near a long straight current-carrying wire. The dimension are shows in the figure. The long wire lies in the plane of the loop. The current in the long wire varies as I = I_(0)(t) . The heat produced in the loop in time t is

Assertion : Specific heat of any substance remains constant at all temperatures. Reason : It is given by s= 1/m * (dQ)/(dt) .

The two ends of a rod of length L and a uniform cross-sectional area A are kept at two temperature T_(1) and T_(2) (T_(1) gt T_(2)) . The rate of heat transfer. (dQ)/(dt) , through the rod in a steady state is given by

At t = 0, switch S is closed, calculate (i) initial rate of increase of current, i.e., (di)/(dt)"at t"=0 . (ii) (di)/(dt) at time when current in the circuit is 0.5A . (iii) Current at t = 0.6 s. (iv) rate at which energy of magnetic field is increasing, rate of heat produced in resistance and rate at which energy is supplied by battery when i = 0.5 A. (v) energy stored in inductor in steady state.

Two moles of an ideal diatomic gas is taken through a process VT^(2)= constant so that its temperature increases by DeltaT=300K . The ratio ((DeltaU)/(DeltaQ)) of increase in internal energy and heat supplied to the gas during the process is