Physics (CDS-Solved Paper)

Burning of a candle is a chemical as well as physical change in which chemical energy is converted into heat and light energy. A light emitting diode, a laser, a television set convert electrical energy into light energy.

The visible portion of the electromagnetic spectrum is light. Visible rays are the most familiar form of electromagnetic waves. It is the part of the spectrum that is detected by human eyes. It runs from about 4 × 10¹⁴ Hz  to 7 × 10¹⁴ Hz or a wavelength of about 700-400 nm. Infrared, radio waves, microwaves, etc., are not visible portion of electromagnetic spectrum

Let s be the distance of object and image, u be the object distance and f be the focal length of the lens. Then, the lens formula,
u = 2f is therefore a minimum. The object and image distances for minimum separation are both 2f, giving separation 4f.

The direction of magnetic field on the earth’s surface is termed as horizontal component of the field.
At a place, it is defined as the component of earth’s magnetic field along the horizontal in the magnetic meridian. Its value is different at different places.
Field declination is the acute angle between magnetic meridian and geographical meridian at a place.
Inclination is the angle which resultant earth’s magnetic field at a place makes with the horizontal surface.

Given, P = 100 W, (power of 1 bulb)
V = 220 V and I = 5 A.
Let x be the maximum number of bulbs that can be safely connected in parallel circuit. Potential difference, V = 220 V
∴ P = VI
100 × = 220 × 5
⇒ x = 220 × 5/100 = 11

Convection is the process of heat transfer of the bulk movement of molecules within fluids such as gases and liquids. In this process, the heat transfers is by the actual motion of matter. It happens in liquid and gases.
Boiling water, land and sea breeze, circulation of air around blast furnace, etc., are the example of convection. Whereas heating of glass surface of a bulb due to current in filament occurs due to conduction of heat.

‘Heat Lost=Heat gained’ represents the relation of principle of calorimetry. According to this principle, if two substances of different temperatures are brought in contact with each other, then heat flows from the substance at higher temperatures to the substances at lower temperatures, till their temperature become equal (equilibrium state). This principle is based on the law of conservation of energy.

When the sun is near the horizon during the morning or evening, it appears reddish due to the scattering of light from the sun near the horizon. It passes through thicker layers of air and covers larger distance in the atmosphere before reaching our eyes. Near the horizon, most of the blue light and shorter wavelengths are scattered away.