NEET 2010 PYQ Mock Test

A tuning fork of frequency $512\text{ Hz}$ makes $4\text{ beats per second}$ with the vibrating string of a piano. The beat frequency decreases to $2\text{ beats per sec}$ when the tension in the piano string is slightly increased. The frequency of the piano string before increasing the tension was:

Which of the following statements is false for the properties of electromagnetic waves?

A lens having focal length $f$ and aperture of diameter $d$ forms an image of intensity $I$. Aperture of diameter $d/2$ in central region of lens is covered by a black paper. Focal length of lens and intensity of image now will be respectively:

A ray of light travelling in a transparent medium of refractive index $\mu$, falls on a surface separating the medium from air at an angle of incidence of $45^{\circ }$. For which of the following values of $\mu$ the ray can undergo total internal reflection?

Two positive ions, each carrying a charge $q$, are separated by a distance $d$. If $F$ is the force of repulsion between the ions, the number of electrons missing from each ion will be ($e$ being the charge on an electron):