Which one of the following statements regarding magnetic field is NOT correct?
- A.Magnetic field is a quantity that has direction and magnitude
- B.Magnetic field lines are closed curves
- C.Magnetic field lines are open curves
- D.No two magnetic field lines are found to cross each other
Correct answer
Explanation
The correct answer is C, Magnetic field lines are open curves. Magnetic field lines are always closed curves, so the statement that they are open curves is the incorrect one.
Outside a magnet, field lines run from the north pole to the south pole; inside the magnet they continue from the south pole back to the north pole, closing the loop. This happens because magnetic poles always come in pairs: no isolated north or south pole has ever been found. The lines are drawn closer together where the field is stronger, as near the poles. The direction of the field at any point is shown by the tangent to the line, which is the way a compass needle points.
A is wrong because it is a correct statement: the magnetic field is a vector, having both size and direction.
B is wrong because it is a correct statement: field lines form closed loops.
D is wrong because it is a correct statement: if two lines crossed, a compass at that point would point two ways at once, which is impossible.
Exam tip: magnetic field lines: closed loops, N to S outside and S to N inside, never cross, crowded where the field is strong.
Practice Questions
View allWhich one of the following is not true for anodizing process?
- A.It makes aluminium corrosion resistant.
- B.Metals like aluminium, titanium and magnesium can be anodized.
- C.Clean aluminium article is the anode and oxygen gas is evolved at the cathode.
- D.It is used in aircraft industry.
Show answer
In anodizing the clean aluminium article is indeed the anode, but oxygen is released at the anode, not at the cathode; hydrogen is released at the cathode.
Read the full explanation →Which one of the following statements is not correct?
- A.The response of the ear to sound of increasing intensity is approximately logarithmic.
- B.The sensitivity of the human ear does not vary with the frequency of the sound.
- C.When two or more waves traverse the same medium, the displacement of any element of the medium is the algebraic sum of the displacements due to each wave.
- D.Longitudinal waves can travel in all media—solids, liquids and gases.
Show answer
The statement that the sensitivity of the human ear does not vary with frequency is false, because the ear is far more sensitive to some frequencies than to others.
Read the full explanation →Kwashiorkor disease in children is caused by
- A.sufficient carbohydrates but less fats in diet
- B.sufficient carbohydrates and fats but deficient proteins in diet
- C.sufficient vitamins but deficient fats in diet
- D.sufficient fats but deficient vitamins in diet
Show answer
Kwashiorkor is a disease of protein deficiency in a child who still gets enough calories. It usually appears when a child is weaned from breast milk onto a starchy diet with little protein.
Read the full explanation →Which one of the following is the correct order of pH for the given substances?
- A.Coffee < Lemon juice < Milk of magnesia < Blood
- B.Milk of magnesia < Blood < Coffee < Lemon juice
- C.Lemon juice < Blood < Coffee < Milk of magnesia
- D.Lemon juice < Coffee < Blood < Milk of magnesia
Show answer
Arranged from most acidic to most basic, the four substances fall in exactly this order. Lemon juice, rich in citric acid, has a pH of about 2 to 2.5.
Read the full explanation →Which one of the following diseases may be caused by the deficiency of vitamin C?
- A.Rickets
- B.Rabies
- C.Hepatitis
- D.Scurvy
Show answer
Scurvy is caused by a lack of vitamin C, or ascorbic acid, which the body needs to make collagen, the protein that holds skin, gums and blood vessels together.
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