A beam of positively charged particles, say A, is going from north to south. On the other hand, a beam of negatively charged particles, say B, is going from south to north. Which one of the following in this respect is correct?
- A.B is deflected towards A.
- B.B is deflected away from A.
- C.B is deflected upwards.
- D.B is deflected downwards.
Correct answer
Explanation
The correct answer is A, B is deflected towards A. Both beams carry conventional current in the same direction, north to south, and parallel currents in the same direction attract each other.
The direction of conventional current is the direction in which positive charges move, and opposite to the direction in which negative charges move. Beam A, positive charges moving north to south, is a current from north to south. Beam B, negative charges moving south to north, is also a current from north to south. Each beam produces a magnetic field around it, and the magnetic force between two parallel currents flowing the same way pulls them together. The electric force between opposite charges is also attractive, so both effects push B towards A.
B is wrong because repulsion happens only for currents flowing in opposite directions. C and D are wrong because the force between two parallel beams acts along the line joining them, not up or down.
Exam tip: like (parallel) currents attract, unlike (antiparallel) currents repel; a negative charge moving one way is a current the other way.
Practice Questions
View allConsider the following pairs : (Commonly used / consumed materials : Unwanted or controversial chemicals likely to be found in them) 1. Lipstick : Lead 2. Soft drinks : Brominated vegetable oils 3. Chinese fast food : Monosodium glutamate Which of the pairs given above is/are correctly matched ?
- A.1 only
- B.2 and 3 only
- C.1 and 3 only
- D.1, 2 and 3
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Each product has been linked to the chemical paired with it. Lead has been found as a trace contaminant in many lipsticks, coming from colour pigments; since lipstick is swallowed in small amounts, regular use raises concern because lead is a toxic heavy metal that harms the nervous system.
Read the full explanation →Which 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.
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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.
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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
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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.
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