Revision Series | Science | General Science | 24

Answer- D

• Sound waves are divided into three categories that cover different frequency range; Audible waves (20 Htz- 20,000 Htz), Infrasonic waves (< 20 Htz) and Ultrasonic waves (> 20,000 Htz).
• Ultrasonic waves are used to destroy insects, clean clothes by removing dust, treat diseases, control automatic doors, detection of aircraft and submarine, determination of depth of sea etc.

Answer- B

• In order for sound to propagate from one place to another, it requires a medium or a fluid to move through.
• The air on the earth allows sound waves to move from one point to another.
• However, there is vacuum on the surface of moon.
• Thus, there is no sound on the moon.

Answer- C

• The heart vibrates at infrasonic sound. We can hear them with the help of stethoscope.
• The speed of sound in solid is maximum.
• Mach number is a quantity that defines how quickly an object travels with respect to the speed of sound.
• The Mach number (M) is simply the ratio of the object’s velocity (V) divided by the speed of sound at the altitude (a).
• Ultrasonic is the name given to sound waves that have frequencies greater than 20,000 Hz. Therefore, statement 1, 3 and 4 are correct.

Answer- C

In a television broadcast, the picture signals are transmitted by amplitude modulation and audio signals are transmitted by frequency modulation.

Answer- B

• A chemical change is a change in which something new is formed (irreversible).
• The starting materials change into an entirely different substance or substances.
• This new substance has a different chemical composition than the starting materials. Examples of chemical change would be the reaction of iron with air (rusting) or the reaction of a metal and acid.
• The crystallization of sodium chloride and melting of ice, both are the examples of a physical change while souring of milk is an example of chemical change.

Answer- A

Both carbohydrate and oxygen are formed in the process of photosynthesis.

Besides leaves, photosynthesis also takes place in other green parts of the plant — in green stems and  green branches.

Desert plants have scales or spine-like leaves to reduce loss of water by transpiration. These plants have green stems which carry out photosynthesis

Answer- D

• Cow milk is yellow in colour because of the presence of carotene.
• Buffalo milk appears whiter than cow milk because it does not contain the yellow pigment carotene.
• Casein is a protein that makes up approximately 80 percent of the total protein content of cow’s milk.
• Existing as globules within the milk and largely responsible for giving milk its white colour.

Answer- C

A gene is the basic physical and functional unit of heredity.

Genes, which consists of DNA, are the genetic material and unit of heredity.

In humans, genes vary in size from a few hundred DNA bases to more than 2 million bases.

Answer- B

Sodium Benzoate is It is widely used as a food preservative, It is the sodium salt of benzoic acid and exists in this form when dissolved in water and its melting point is 410°C.

Answer- D

• Chromatography is a separation technique used to separate the different components in a liquid mixture.
• The separation is based on differential partitioning between the mobile and stationary phases. Chromatography may be preparative or analytical. The purpose of preparative chromatography is to separate the components of a mixture for more advanced use and thus it is a form of purification.