Correct Answer: B. The electric potential energy of a negatively charged particle increases when it moves to a point of lower potential .

Explanation

The potential energy for a positive charge increases when it moves against an electric field. And decreases when it moves with the electric field; The opposite is true for a negative charge. Unless the unit charge crosses a changing magnetic field, its potential at any given point does not depend on the path taken.

Correct Answer: B. i, ii, iii only

Correct Answer: C) diffraction

Explanation

(a)Definition of diffusion; The process by which molecules of different substances move randomly among one another.

OR

Intimate mixing of molecules/atoms/particles of different substance (as a result of kinetic energy)

(b)Factors that affect the rate of diffusion

- density of substance

- mass of substance

- temperature

Correct Answer: C. 5N 37° north of east

Correct Answer: D. 638mm

Explanation

Let \(h_{Q}\) and \(\rho_{Q}\) be the least length and the density of \(Q_{1}\)

while \(h\) and \(\rho\) are the length and density of mercury respectively.

\(h\times \rho \times g = h_{Q} \times \rho_{Q} \times g\)

\(76cm \times 13.6 \times 10 = h_{Q} \times 16.2 \times 10\)

\(h_{Q} = \frac{76\times13.6\times10}{16.2\times10}\)

\(h_{Q} = \frac{10336}{162}\)

\(h_{Q} \approxeq 63.8cm = 638mm\)

Explanation

(a)(i)

Mode of Operation:

In the X-ray tube a Low voltage high p.d is applied between the hot cathode and the anode. Electrons are emitted from the cathode and are accelerated to an extremely high speed. They are suddenly decelerated when they strike the anode causing the emission of high - energy radiation of short wavelength - X-ray. In this process the anode becomes very hot, and requires cooling fins on the outside of the tube.

Energy Transformation: The electrons have kinetic energy which is partly changed to internal energy (potential) and finally changed to heat energy.

(b) Hardness: Refers to X-rays with high penetrating power, short wavelength but high frequency. They are produced by increasing the p.d. between the cathode and anode. Such X-rays are called hard X-rays. Less penetrating or lower frequency ones are called soft X-rays. They are produced at lower p.d.

Intensity: High intensity X-rays beam results from the increase of current through the filament which leads to increase in the number of electrons.

(c)(i) Uses of X-rays:

(1) Investigating the structure of crystals ; (2) X-ray examination of the body for broken bones; (3) As invincible bullets for the treatment of tumours ; (4) Examination of metals for defects and fractures.

(ii) They may cause damage to living tissue and to cells. Precaution to be taken includes lead screening and regular health checks.

Correct Answer: B. Pressure in liquids and gases

Correct Answer: B. painting it black

Correct Answer: C. ensures that only dry steam gets into the calorimeter