SOME IMPORTANT PHYSICS AND MATHEMATICS QUESTIONS FOR JEE MAINS-2019

Q 1. An aluminium ring B faces an electromagnet A. The current / through A can be altered.

If current is passed through solenoid A as shown. Current entering at end A is clockwise. When seen from the side of A, so it develops south polarity at A and north polarity at B. When current / through A increase, it is like north of the magnet approaching the ring B and due to Lenz’s law face of ring B facing B develops north polarity and hence there is repulsion between the two.

Q 2. The current in the winding on a torpid is 4.0 A. There are 200 turns and the mean circumferential length is 20 cm. If the inside magnetic field is 2.0 T, the relative permeability is near to

Options:

(a) 1000                   

(b) 2500                   

(c) 2000                   

(d) 4000

Ans. Option (b) is correct

Q 3. A metallic rod of length ‘l’is tied to a string of length ‘2l’ and made to rotate with angular speed on a horizontal table with one of the string fixed. If there is a vertical magnetic field B in the region, the emf induced across the ends of the rod is

Ans. Option (d) is correct

Q 4. A circular loop of radius 0.4 cm lies parallel to a much bigger circular loop of radius 40 cm. The centre of the smaller loop is on the axis of the bigger loop. The distance between their centres is 25 cm. If a current of 4.0 A flows through the bigger loop, then the flux linked with smaller loop is

Q 5. A current carrying infinitely long wire is kept along the diameter of a circular wire loop, without touching it. The correct statement (s) is / (are)

Options:

(a) The emf induced in the loop is zero if the current is constant

(b) The emf induced in the loop is finite if the current is constant

(c) The emf induced in the loop is zero if the current decreases at a steady rate

(d) The emf induced in the loop is finite if the current decreases at a steady rate

Ans. Option (d) is correct

Explanation:

Due to current in the straight wire, net magnetic flux from the circular loop is zero. This is because; magnetic field is inward in half of the circle and outward in the other half of the circle. Therefore, change in current will not cause any change in magnetic flux from the loop. Therefore, induced emf under all condition through the circular loop is zero.