Which one of the following statements is not correct ?
- A.An electric motor converts electrical energy into mechanical energy.
- B.An electric generator works on the principle of electromagnetic induction.
- C.The magnetic field at the centre of a long circular coil carrying current will be parallel straight lines.
- D.A wire with a green insulation is usually the live wire of an electric supply.
Correct answer
Explanation
The correct answer is D. In household wiring the wire with green insulation is the earth wire, not the live wire, so this statement is not correct.
Domestic supply in India uses three wires. Under the colour code taught in school textbooks, the live wire has red insulation, the neutral wire black and the earth wire green; newer wiring uses brown for live, blue for neutral and green-yellow for earth. The earth wire connects the metal body of an appliance to the ground, so that a leaking current flows safely into the earth instead of giving the user a shock. Green is therefore never used for the live wire.
A is wrong: an electric motor does convert electrical energy into mechanical energy, so this statement is correct.
B is wrong: a generator does work on electromagnetic induction, discovered by Faraday, so this statement is correct.
C is wrong: inside a long coil carrying current (a solenoid) the field lines are parallel straight lines, showing a uniform field, so this statement is correct.
Exam tip: live = red (brown), neutral = black (blue), earth = green (green-yellow).
Practice Questions
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- A.haploid zygote
- B.diploid zygote
- C.non-motile male gametes
- D.motile male gametes
Show answer
Syngamy is the fusion of a male and a female gamete, and since each gamete is haploid, their union gives a diploid zygote.
Read the full explanation →Human insulin molecule is composed of one α-chain having 21 amino acids and one β-chain having 30 amino acids. How many functional insulin genes occur in adult humans?
- A.One
- B.Two
- C.Three
- D.Four
Show answer
Humans have a single functional insulin gene, INS, on the short arm of chromosome 11, and both chains of insulin come from it.
Read the full explanation →Which one of the following is the value of one nanometer?
- A.10⁻⁷ cm
- B.10⁻⁶ cm
- C.10⁻⁴ cm
- D.10⁻³ cm
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One nanometre is 10⁻⁹ metre, and since one metre is 100 (10²) centimetres, it equals 10⁻⁷ centimetre. The prefix nano means one billionth.
Read the full explanation →Which of the following is the general formula for saturated hydrocarbons?
- A.CₙH₂ₙ₊₂
- B.CₙH₂ₙ₋₂
- C.CₙH₂ₙ₊₁
- D.CₙH₂ₙ₋₁
Show answer
Saturated open-chain hydrocarbons are the alkanes, and every alkane fits the formula CₙH₂ₙ₊₂. In a saturated hydrocarbon every carbon atom is joined to others only by single bonds, so each carbon holds the largest possible number of hydrogen atoms.
Read the full explanation →Which one of the following is not an epidemic disease?
- A.Cholera
- B.Malaria
- C.Smallpox
- D.Elephantiasis
Show answer
Elephantiasis, or lymphatic filariasis, is an endemic disease: it stays steadily present in certain regions and develops slowly over years, rather than breaking out suddenly in a large number of people.
Read the full explanation →