81. How much should minimum distance be between the source of sound and reflecting surface, so that an echo can be heard clearly?
1. 10 meter
2. 17 meter
3. 24 meter
4. 30 meter
Option “2” is correct. The repetition of sound produced due to the reflection from a large surface like wall, hill or mountain is called echo. Minimum distance between source of sound and reflecting surface be 17 meter so that an echo can be heard.
82. Consider the following statements about ultrasonic waves:
1. They can destroy insects.
2. They can clean clothes by removing dust.
3. They can be used to treat diseases.
4. They can control automatic doors.
Of the above statements
1. 1 and 2 are correct
2. 3 and 4 are correct
3. 1, 2 and 3 are correct
4. All are correct
Option “4” is correct. Sound waves are divided into three categories that cover different frequency range; Audible waves (20 Hz- 20,000 Hz), Infrasonic waves (<20 Hz) and Ultrasonic waves (>20,000 Hz). 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.
83. What is the SI unit of intensity of sound?
1. Decibel
2. Newton
3. Hertz
4. Tesla
Option “1” is correct. Decibel(dB) is the SI unit of intensity of sound.
84. Which colour is formed when Blue and Green are mixed?
1. Cyan
2. Brown
3. Black
4. Violet
Option “1” is correct. When blue and green colour combine, the result is cyan.
85. What is the SI unit of Power?
1. Boyle
2. Watt
3. Newton
4. Pascal
Option “2” is correct. SI unit of power is watts. A watt is the power that it takes to do one joule of work in one second.
86. The gas used in discharge tubes for optical decoration and advertising is-
Option “4” is correct. The neon gas is used in discharge lamps, tubes and in fluorescent bulbs.
87. The distance-time graph for the motion of an object moving with a constant speed is a __________.
1. Dot
2. Circle
3. Straight Line
4. Curve
Option “3” is correct. The distance-time graph for the motion of an object moving with a constant speed is a Straight Line.
88. If the force applied on the object is in the direction of its motion, the speed of the object __________.
1. Increases
2. Stops
3. Decreases
4. No effect
Option “1” is correct. If the force applied on the object is in the direction of its motion, the speed of the object increases.
89. Sphygmomanometer measures the blood pressure in the-
1. Veins
2. Arteries
3. Eyes
4. Synovial
Option “2” is correct. Blood pressure is measured by instrument called sphygmomanometer also called as blood pressure meter, it is used to measure the pressure of blood in Arteries.
