Sound Navigation and Ranging (SONAR) is used to detect underwater objects. For this, its transmitter produces
- A.microwaves
- B.visible light
- C.ultrasonic waves
- D.infrared radiation
Correct answer
Explanation
The correct answer is C, ultrasonic waves. SONAR sends out pulses of high-frequency sound, above 20 kHz, which travel well through water and bounce back from objects.
The transmitter sends ultrasonic pulses into the water, and a detector picks up the echo reflected from the sea bed, a submarine, a shipwreck or a shoal of fish. Knowing the speed of sound in sea water (about 1,500 m/s) and the time t taken by the echo, the distance is found as d = v × t ÷ 2, since the sound goes to the object and back. Ultrasound is chosen because its short wavelength gives sharp echoes and it can be sent in a narrow beam.
A is wrong because microwaves are electromagnetic waves used in radar and ovens, and water absorbs them strongly. B is wrong because visible light fades within a short depth of sea water. D is wrong because infrared radiation is also absorbed quickly by water and is used for heat sensing and remote controls.
Exam tip: SONAR = ultrasound under water; RADAR = radio waves or microwaves in air; distance = speed × time ÷ 2.
Practice Questions
View allConsider the following pairs : (Commonly used / consumed materials : Unwanted or controversial chemicals likely to be found in them) 1. Lipstick : Lead 2. Soft drinks : Brominated vegetable oils 3. Chinese fast food : Monosodium glutamate Which of the pairs given above is/are correctly matched ?
- A.1 only
- B.2 and 3 only
- C.1 and 3 only
- D.1, 2 and 3
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Each product has been linked to the chemical paired with it. Lead has been found as a trace contaminant in many lipsticks, coming from colour pigments; since lipstick is swallowed in small amounts, regular use raises concern because lead is a toxic heavy metal that harms the nervous system.
Read the full explanation →Which one of the following is not true for anodizing process?
- A.It makes aluminium corrosion resistant.
- B.Metals like aluminium, titanium and magnesium can be anodized.
- C.Clean aluminium article is the anode and oxygen gas is evolved at the cathode.
- D.It is used in aircraft industry.
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In anodizing the clean aluminium article is indeed the anode, but oxygen is released at the anode, not at the cathode; hydrogen is released at the cathode.
Read the full explanation →Which one of the following statements is not correct?
- A.The response of the ear to sound of increasing intensity is approximately logarithmic.
- B.The sensitivity of the human ear does not vary with the frequency of the sound.
- C.When two or more waves traverse the same medium, the displacement of any element of the medium is the algebraic sum of the displacements due to each wave.
- D.Longitudinal waves can travel in all media—solids, liquids and gases.
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The statement that the sensitivity of the human ear does not vary with frequency is false, because the ear is far more sensitive to some frequencies than to others.
Read the full explanation →Kwashiorkor disease in children is caused by
- A.sufficient carbohydrates but less fats in diet
- B.sufficient carbohydrates and fats but deficient proteins in diet
- C.sufficient vitamins but deficient fats in diet
- D.sufficient fats but deficient vitamins in diet
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Kwashiorkor is a disease of protein deficiency in a child who still gets enough calories. It usually appears when a child is weaned from breast milk onto a starchy diet with little protein.
Read the full explanation →Which one of the following is the correct order of pH for the given substances?
- A.Coffee < Lemon juice < Milk of magnesia < Blood
- B.Milk of magnesia < Blood < Coffee < Lemon juice
- C.Lemon juice < Blood < Coffee < Milk of magnesia
- D.Lemon juice < Coffee < Blood < Milk of magnesia
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Arranged from most acidic to most basic, the four substances fall in exactly this order. Lemon juice, rich in citric acid, has a pH of about 2 to 2.5.
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