Ray Optics and Optical Instruments — Physics STD 12 Science — Question

Number of spectral lines in hydrogen atom is    

(a) 3

(b) 6

(c) 15

(d) Infinite

The angular speed of the electron in the nth orbit of Bohr hydrogen atom is?

Mark the correct statements for a particle going on a straight line:

1. If the velocity and acceleration have opposite sign, the object is slowing down.
2. If the position and velocity have opposite sign, the particle is moving towards the origin.
3. If the velocity is zero at an instant, the acceleration should also be zero at that instant.
4. If the velocity is zero for a time interval, the acceleration is zero at any instant within the time interval.

The output in the circuit of figure is taken across a capacitor. It is as shown in figure

(a)

(b)

(c)

(d)

An object approaches a convergent lens from the left of the lens with a uniform speed 5 m/s and stops at the focus. The image

Electron volt (ev) is the unit of:

The dimensions of polarisation are:

Half life of radioactive element depends upon

(a) Amount of element present	(b) Temperature
(c) Pressure	(d) Nature of element

The spectra used to identify the elements in the mixture is:

A conducting circular loop of radius r carries a constant current i. It is placed in a uniform magnetic field , such that   is perpendicular to the plane of the loop. The magnetic force acting on the loop is

(a) ir

(b) 2πri

(c) Zero

(d) πri