Physics Heat Optics

Explanation

The temperature at which food is cooked in a pressure cooker depends mainly on the area of the hole in the lid, the temperature of the flame, and the weight of the lid. These factors collectively affect the pressure inside the cooker, which in turn influences the boiling point of water and the cooking temperature.

Explanation

Sodium lamps emit light in a 360-degree pattern, while LED lamps emit light directionally. Sodium lamps produce almost monochromatic light, whereas LED lamps offer a wider spectrum of visible light, providing significant color advantages in street-lighting.

Explanation

Visible Light Communication (VLC) technology utilizes wavelengths in the electromagnetic spectrum from 375 to 780nm. VLC is a form of optical wireless communication that can transmit large amounts of data quickly, outperforming Bluetooth in speed. Unlike some other wireless technologies, VLC is not affected by electromagnetic interference. Therefore, the correct statements are 1, 3, and 4, making the answer option (c).

Explanation

In the given list of phenomena, the size of the sun at dusk, the color of the sun at dawn, and the twinkle of stars in the sky are all optical illusions. The size of the sun at dusk appears larger due to atmospheric refraction, the color of the sun at dawn looks yellow because of scattering, and the twinkling of stars is also an optical illusion.

Explanation

In a night vision apparatus, infra-red waves are utilized to enable vision in complete darkness and improve visibility in low-light conditions.

Explanation

Crookes glass is the type of glass that can block ultraviolet rays because it is made with cerium and rare earth elements that absorb this type of radiation.

Explanation

In an air-conditioner, heat is taken out from the room air at the evaporator coils and released outside at the condenser coils. This process helps in cooling the room and removing humidity. So, the correct statement is only statement 3.

Explanation

Explanation: The statement made in Assertion is incorrect. When the temperature of a liquid like glycerine increases, its viscosity actually decreases rather than increases. This is due to the fact that as temperature rises, the kinetic energy of the molecules in the liquid also increases, leading to a decrease in viscosity and an increase in fluidity.

Explanation

In this scenario, the hollow sphere, hollow cube, and thin circular plate, all made of the same material and heated to 20°C above room temperature, are left to cool in the room. The sphere will reach room temperature first due to its maximum surface area, as heat loss is directly related to surface area.

Explanation

In the natural world, various phenomena like terrestrial heating, reflection of light, refraction of light, and diffraction of light occur. A mirage is formed due to the combination of terrestrial heating and refraction of light. When the ground heats up, it causes the air above it to become warmer and less dense, leading to the refraction of light rays and the creation of a mirage.

Explanation

Both Assertion and Reason are correct. When both a piece of copper and a piece of glass are heated to the same temperature, the copper piece feels hotter to touch than the glass piece. This is because copper, being a metal, is a better conductor of heat compared to glass, which is a poor conductor. The reason for the difference in perceived temperature is due to the varying thermal conductivity of the materials.

Explanation

When water is heated from 0°C to 10°C, its volume first decreases from 0°C to 4°C due to contraction. This initial decrease is followed by an increase in volume beyond 4°C to 10°C as the water molecules gain kinetic energy and move more randomly.

Explanation

When light waves transition from air to glass, the properties that change are wavelength and velocity.

Explanation

Endoscopy is a medical diagnostic technique that involves using an endoscope to look inside the body by utilizing the principle of total internal reflection of light.

Explanation

When sunlight falls on a CD, rainbow-like colors are observed due to the presence of a clear plastic coating on the surface. This phenomenon can be explained by the combined effects of refraction, diffraction, and transmission of light through the CD.

Explanation

In this situation, when strips of metals A and B are joined together and heated, metal A expands more than metal B. As a result, the jointed strip will bend downward. This is because the volume expansion of metal A is greater than that of metal B when the same amount of heat is applied.

Explanation

Cryogenics, a field of physics, focuses on achieving extremely low temperatures (below 150 °C, -238 °F or 123 K) and studying how materials behave at such cold temperatures.

Explanation

When a liquid drop is released from external forces, it naturally contracts and takes on a spherical shape. This behavior is caused by surface tension, a property of liquids that drives them to minimize their surface area.

Explanation

Optical fibre operates based on the principle of total internal reflection. It is a slender, pliable, see-through fibre that serves as a channel for light to travel between its two ends.