21.

The false statement is

• Every SHM is periodic in nature

• Every periodic motion is SHM

• In every SHM, total energy is proportional to the square of amplitude

• In SHM, acceleration of oscillating body is proportional to the displacement from the equilibrium position

A particle of unit mass and specific charge s is thrown from the wall perpendicularly to a wall at a distance d from the wall with speed 'v'. The minimum magnetic field produced so that the particle does not touch the wall, is:

• $\frac{\mathrm{v}}{\mathrm{sd}}$

• $\frac{2\mathrm{v}}{\mathrm{sd}}$

• $\frac{\mathrm{v}}{2\mathrm{sd}}$

• $\frac{\mathrm{v}}{4\mathrm{sd}}$

An electron beam is accelerated through a potential difference of V volt. The minimum wavelength of X-rays produced is :

• $\frac{\mathrm{he}}{\mathrm{cV}}$

• $\frac{\mathrm{cV}}{\mathrm{he}}$

• $\frac{\mathrm{eV}}{\mathrm{hc}}$

• $\frac{\mathrm{hc}}{\mathrm{eV}}$

Light waves of wavelength $\mathrm{\lambda }$ is incident on a metal of work function $\phi$ . Maximum velocity of the electron is :

• ${\left[\frac{2(\mathrm{h\lambda }-\mathrm{\phi })}{\mathrm{m}}\right]}^{1/2}$

• ${\left[\frac{2(\mathrm{hc}-\mathrm{\lambda \phi })}{\mathrm{m\lambda }}\right]}^{1/2}$

• $\frac{2(\mathrm{hc}-\mathrm{\lambda \phi })}{\mathrm{m}}$

• ${\left[\frac{\mathrm{hc}+\mathrm{\lambda \phi }}{\mathrm{m\lambda }}\right]}^{1/2}$

A charged particle is moving in a uniform magnetic field in a circular path of radius R. When energy of the particle is doubled, then the new radius will be:

• R

• R$\sqrt{2}$

• R/$\sqrt{2}$

•  2R

A capacitor of capacity C is charged by connecting it with R according to the figure. Energy supplied by the battery in this process is :

• more than $\frac{1}{2}C{V}^2$

• $\frac{1}{2}{\mathrm{CV}}^2$

• 2CV²

• less than $\frac{1}{2}{\mathrm{CV}}^2$

If a current is flowing in a spring, then it:

• compress

• swing

• expand

• remain unaffected

Two bulbs A and B are connected in parallel. Bulb A will glow more than bulb B. If their resistances are R_A and R_B respectively. Then :

• R_A $<$ R_B

• R_A $=$ R_B

• R_A $>$ R_B

• none of these

Magnetic and electric field are acting on a proton moving with velocity $\mathrm{\nu }$. Proton will be undeflected if 

• E is parallel to v, but perpendicular to B

• E and B both are parallel to v

• E and B are perpendicular to each other

• E, B and v are perpendicular to one another and v=$\frac{\mathrm{E}}{\mathrm{B}}$

The unit of permittivity (${\mathrm{\epsilon }}_0$) of space is

• newton-metre² / coulomb²

• coulomb / newton-metre

• coulomb / newton-metre²

• coulomb² / newton-metre²