To protect steel and iron from rusting, a thin layer of which one of the following metals is applied?
- A.Magnesium
- B.Zinc
- C.Aluminium
- D.Lead
Correct answer
Explanation
The correct answer is B, Zinc. Coating iron or steel with a thin layer of zinc is called galvanisation, and it is the most common way to protect them from rusting.
Rust forms when iron reacts with oxygen and moisture to make hydrated iron oxide. In galvanisation the article is usually dipped in molten zinc, which forms a firm coating that keeps air and water away. Zinc also protects the iron even where the coating is scratched, because zinc is more reactive than iron and corrodes first, a process called sacrificial protection. Galvanised iron sheets, pipes, buckets and wires are common examples. Other ways to prevent rust include painting, oiling, tinning and alloying iron into stainless steel.
A is wrong because magnesium, though used as a sacrificial block for ships and pipelines, is not applied as a thin coating on iron articles. C is wrong because aluminium protects itself with an oxide layer but is not the usual coating for iron. D is wrong because lead is toxic and is not used to galvanise iron.
Exam tip: zinc coating on iron, galvanisation; tin coating, tinning; stainless steel, iron with chromium and nickel.
Practice Questions
View allWhich of the following statements about electromagnetic waves, sound waves and water waves is/are correct ? 1. They exhibit reflection 2. They carry energy 3. They exert pressure 4. They can travel in vacuum Select the correct answer using the code given below :
- A.1,2 and 3
- B.2 and 4
- C.1 and 3 only
- D.1 only
Show answer
All three kinds of wave reflect, carry energy and exert pressure, but only electromagnetic waves can travel through a vacuum.
Read the full explanation →Which one of the following is NOT the unit of energy?
- A.Joule
- B.Watt-hr
- C.Newton-metre
- D.kg-metre/sec²
Show answer
A kilogram-metre per second squared is mass times acceleration, which is force; it is the newton, not a unit of energy.
Read the full explanation →In an electric circuit, a wire of resistance 10 Ω is used. If this wire is stretched to a length double of its original value, the current in the circuit would become :
- A.half of its original value.
- B.double of its original value.
- C.one-fourth of its original value.
- D.four times of its original value.
Show answer
Stretching the wire to twice its length makes its resistance four times larger, so at the same voltage the current falls to a quarter.
Read the full explanation →Which one of the following scientists mentioned that an electron in an atom could revolve in certain stable orbits without the emission of radiant energy ?
- A.Ernest Rutherford
- B.J.J. Thomson
- C.Niels Bohr
- D.Albert Einstein
Show answer
In his 1913 model of the atom, Bohr proposed that electrons move in certain fixed orbits, called stationary states, in which they do not radiate energy.
Read the full explanation →In a solenoid, the current flowing through the wire is I and number of turns per unit length is n. This gives a magnetic field B inside the solenoid. If number of turns per unit length is increased to 2n, what will be the value of magnetic field in the solenoid ?
- A.B
- B.2B
- C.B/2
- D.B/4
Show answer
The field inside a long solenoid is directly proportional to the number of turns per unit length, so doubling n doubles the field.
Read the full explanation →