Which one of the following frequency ranges is sensitive to human ears ?
- A.0-200 Hz
- B.20-20,000 Hz
- C.200-20,000 Hz only
- D.2,000-20,000 Hz only
Correct answer
Explanation
The correct answer is B, 20-20,000 Hz. The normal human ear hears sound from about 20 hertz to 20,000 hertz, the audible range.
Frequency, measured in hertz, is the number of vibrations per second, and it decides the pitch of a sound: the higher the frequency, the shriller the note. Our ears respond to the band from 20 Hz to 20 kHz, and are most sensitive between roughly 2,000 and 5,000 Hz. The upper limit falls with age, so older adults often cannot hear the highest notes. Sound below 20 Hz is called infrasound and sound above 20 kHz ultrasound; both exist all around us but our ears cannot detect them.
A is wrong because 0-200 Hz includes infrasound below 20 Hz, which we cannot hear, and misses most of the audible band.
C is wrong because the word "only" shuts out 20-200 Hz, low notes we can hear.
D is wrong for the same reason: it leaves out everything from 20 to 2,000 Hz, which includes much of human speech.
Exam tip: audible range 20 Hz-20 kHz; pitch depends on frequency, loudness on amplitude.
Practice Questions
View allThe frequency of ultrasound waves is
- A.less than 20 Hz
- B.between 20 Hz and 2 kHz
- C.between 2 kHz and 20 kHz
- D.greater than 20 kHz
Show answer
Ultrasound is sound with a frequency above 20,000 Hz, the upper limit of human hearing. Humans hear sound between about 20 Hz and 20 kHz.
Read the full explanation →Which one of the following is an example of a clean fuel ?
- A.Coke
- B.Propane
- C.Petrol
- D.Wax
Show answer
Propane is a light gaseous hydrocarbon that burns completely with a blue flame, leaving no smoke, soot or ash. A clean fuel burns completely, gives high heat and releases few pollutants.
Read the full explanation →A sample of 'soft soap' contains
- A.Caesium
- B.Potassium
- C.Calcium
- D.Magnesium
Show answer
Soft soaps are potassium salts of fatty acids, while ordinary hard bar soaps are sodium salts. Soap is made by saponification, heating an oil or fat with an alkali.
Read the full explanation →Which of the following sets of elements has the same valency?
- A.Na, Mg, Ca
- B.Na, Mg, Al
- C.Mg, Ca, K
- D.Mg, Ca, Ba
Show answer
Magnesium, calcium and barium are all alkaline earth metals of group 2, and each has a valency of 2. Elements in the same group of the periodic table have the same number of electrons in their outermost shell, and so the same valency.
Read the full explanation →Which one of the following is the correct order of the valencies of elements Ne, Si, N and Mg?
- A.Ne < Mg < N < Si
- B.Si < N < Mg < Ne
- C.Ne < N < Si < Mg
- D.Mg < Ne < N < Si
Show answer
Their valencies are neon 0, magnesium 2, nitrogen 3 and silicon 4. Valency is the combining capacity of an atom, the number of electrons it loses, gains or shares to reach a stable octet.
Read the full explanation →