The presence of magnetic field can be determined using which one of the following instruments?
- A.Ammeter
- B.Voltmeter
- C.Magnetic needle
- D.Motor
Correct answer
Explanation
The correct answer is C, Magnetic needle. A freely pivoted magnetic needle turns to line up with any magnetic field around it, so its deflection shows that a field is present and which way it points. A compass is simply a small magnetic needle balanced on a pivot. Away from other magnets it settles along the Earth's north-south field, and near a magnet or a current-carrying wire it swings to a new direction. Hans Christian Oersted found in 1820 that a current deflects a compass needle, the first proof that electricity produces magnetism, and plotting compass directions is how field lines are drawn in the classroom. Option A is wrong because an ammeter measures electric current in a circuit. Option B is wrong because a voltmeter measures the potential difference between two points. Option D is wrong because a motor uses a magnetic field to turn electrical energy into motion; it is a machine, not a detector. Exam tip: compass needle detects a field; ammeter = current, voltmeter = voltage.
Practice Questions
View allThe rate of evaporation of liquid does not depend upon
- A.temperature
- B.its surface area exposed to the atmosphere
- C.its mass
- D.humidity
Show answer
Evaporation is a surface process, so its rate depends on conditions at the surface of the liquid, not on how much liquid there is in total.
Read the full explanation →Which one of the following is considered as a compound ?
- A.Silicon
- B.Tin
- C.Sugar solution
- D.Calcium carbonate
Show answer
Calcium carbonate, CaCO3, is a compound because calcium, carbon and oxygen are chemically combined in it in a fixed ratio.
Read the full explanation →'Altitude sickness' is caused at high altitude due to
- A.high partial pressure of oxygen
- B.low partial pressure of oxygen
- C.low level of haemoglobin
- D.high partial pressure of carbon dioxide
Show answer
As one climbs, air pressure falls, so each breath delivers oxygen at a lower partial pressure and less of it passes from the lungs into the blood.
Read the full explanation →Which one of the following is not a characteristic of a compound?
- A.Composition is variable.
- B.All particles of compound are of only one type.
- C.Particles of compound have two or more elements.
- D.Its constituents cannot be separated by simple physical methods.
Show answer
A compound always has a fixed composition by mass, so a variable composition is a property of mixtures, not compounds.
Read the full explanation →A positively charged particle (alpha-particle) is projected towards west in a horizontal plane. It is deflected towards north in the same plane by a magnetic field. Which one among the following is the direction of the magnetic field?
- A.Towards south
- B.Towards east
- C.Vertically downwards
- D.Vertically upwards
Show answer
The magnetic force on a moving charge is F = q(v × B), and only an upward field turns a westward-moving positive charge towards the north.
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