The device used to produce electric current is known as
- A.motor
- B.generator
- C.ammeter
- D.galvanometer
Correct answer
Explanation
The correct answer is B, generator. An electric generator converts mechanical energy into electrical energy and so produces electric current.
A generator works on electromagnetic induction, discovered by Michael Faraday in 1831. When a coil rotates in a magnetic field, the magnetic flux through it keeps changing, and this induces a current in the coil. An AC generator uses slip rings and gives alternating current, while a DC generator uses a split-ring commutator and gives direct current. Power stations, whether driven by steam, water or wind, all use large generators to produce the electricity we use.
A is wrong because a motor does the reverse job; it turns electrical energy into mechanical energy. C is wrong because an ammeter only measures the current flowing in a circuit and is connected in series. D is wrong because a galvanometer only detects the presence and direction of a small current.
Exam tip: generator means mechanical to electrical, motor means electrical to mechanical; both rest on Faraday's work.
Practice Questions
View allWho among the following built a model steam engine in 1698 called "Miner's Friend" to drain mines ?
- A.Thomas Savery
- B.Thomas Newcomen
- C.James Watt
- D.Richard Arkwright
Show answer
The English engineer Thomas Savery patented a steam pump in 1698 and called it the Miner's Friend, as it was meant to pump water out of flooded mines.
Read the full explanation →A metallic wire having resistance of 20 Ω is cut into two equal parts in length. These parts are then connected in parallel. The resistance of this parallel combination is equal to
- A.20 Ω
- B.10 Ω
- C.5 Ω
- D.15 Ω
Show answer
Each half of the wire has a resistance of 10 Ω, and two 10 Ω resistors in parallel give 5 Ω. The resistance of a wire is R = ρL/A, so it is directly proportional to its length when the material and thickness stay the same.
Read the full explanation →Myopia is a defect in human vision where an image of a
- A.nearby object is focused beyond the retina.
- B.nearby object is focused before the retina.
- C.distant object is focused before the retina.
- D.distant object is focused beyond the retina.
Show answer
In myopia, or short-sightedness, a person sees near objects clearly but distant objects look blurred because their image forms in front of the retina.
Read the full explanation →A homogeneous mixture contains two liquids. How are they separated ?
- A.By filtration
- B.By evaporation
- C.By distillation
- D.By condensation
Show answer
Two miscible liquids that form a homogeneous mixture are separated by distillation, which uses the difference in their boiling points.
Read the full explanation →Cartilage is NOT found in
- A.larynx
- B.nose
- C.ear
- D.urinary bladder
Show answer
The urinary bladder is a hollow muscular sac made of smooth muscle and a stretchable lining; it has no cartilage.
Read the full explanation →