CBSE Class 12 Physics Magnetic Effects of Current Assignment

2 marks

Question. An electric current passes through a long straight wire. At a distance 10 cm from the wire , the magnetic field is 8T. Find the magnetic field at 80cm from the wire.
Answer. 1𝑇 (𝐻𝑖𝑛𝑡∶𝐵∝1/𝑟)

Question. A straight wire of length ‘L’ carrying a current ‘I’ stays suspended horizontally in mid-air in a region where there is a uniform magnetic field𝐵⃗⃗. The linear mass density of the wire is 𝜆. Obtain the magnitude and direction of the magnetic field.
Answer. 𝐷𝑖𝑟𝑒𝑐𝑡𝑖𝑜𝑛−𝐻𝑜𝑟𝑖𝑧𝑜𝑛𝑡𝑎𝑙 𝑎𝑛𝑑 𝑝𝑒𝑟𝑝𝑒𝑛𝑑𝑖𝑐𝑢𝑙𝑎𝑟 𝑡𝑜 𝑡ℎ𝑒 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑡ℎ𝑒 𝑤𝑖𝑟𝑒. 𝐵=𝜆𝑔/𝐼

Question. A galvanometer of resistance 25Ω is shunted by a 2.5Ω wire. Find the part of total current that flows through the galvanometer .
Answer. 𝐼𝑔/𝐼=1/11

Question. The scale of a galvanometer of resistance 100Ω contains 25 divisions. It gives a deflection of one division on passing a current of 4×10⁻⁴𝐴. Find the resistance required to convert it into a voltmeter of range 2.5𝑉.
Answer. 150Ω

Question. A galvanometer coil has a resistance of 10Ω and the metre shows full scale deflection for a current of 1𝑚𝐴.Find the shunt resistance required to convert the galvanometer into an ammeter of range 0-100mA.
Answer. (0.1Ω)

Question. Which one of the following will describe the smallest circle when projected with the same velocity 𝑣 perpendicular to the magnetic field 𝐵 : (i) 𝛼 particle, and (ii) 𝛽 particle?
Answer. ( 𝛽 𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒.𝐻𝑖𝑛𝑡: 𝑟 ∞𝑚/𝑞)

3 Marks

Question. A long wire with a small current element of 6mm is placed at the origin and carries a current of 2A along the X-axis. Find the magnitude and direction of the magnetic field due the element on the Y axis at a distance 0.2m from it.
Answer. 𝐵=3×10⁻⁸𝑇
Direction – Perpendicular to the plane of the paper outwards. 𝐻𝑖𝑛𝑡∶𝐵𝑖𝑜𝑡−𝑆𝑎𝑣𝑎𝑟𝑡 𝑙𝑎𝑤 𝑒𝑞𝑢𝑎𝑡𝑖𝑜𝑛

Question. To increase the current sensitivity of a moving coil galvanometer by 50%, its resistance is increased so that the new resistance becomes twice its initial resistance. By what factor does its voltage sensitivity change?
Answer. 𝑉𝑠,=0.75𝑉𝑠;𝑣𝑜𝑙𝑡𝑎𝑔𝑒 𝑠𝑒𝑛𝑠𝑖𝑡𝑖𝑣𝑖𝑡𝑦 𝑑𝑒𝑐𝑟𝑒𝑎𝑠𝑒𝑠 𝑏𝑦 25%.

Question. A galvanometer can be converted into a voltmeter of certain range by connecting a resistance of 980Ω in series with it. When the resistance is 470Ω connected in series, the range is halved. Find the resistance of the galvanometer.
Answer. 𝐺=40Ω
𝐻𝑖𝑛𝑡: 𝑉/(980+𝐺)=𝑉/2(470+𝐺)

ASSERTION REASONING QUESTIONS

Two statements are given-one labelled Assertion (A) and the other labelled Reason (R). While answering these questions, you are required to choose any one of the following four responses. (a) If both Assertion and Reason are correct and the Reason is a correct explanation
of the Assertion. (b) If both Assertion and Reason are correct but Reason is not a correct explanation
of the Assertion. (c) If the Assertion is correct but Reason is incorrect. (d) If both the Assertion and Reason are incorrect.

Question. Assertion: When radius of circular loop carrying current is doubled, its magnetic moment becomes four times.
Reason: Magnetic moment depends on area of the loop.
Answer. A

Question. Assertion: When a magnetic dipole is placed in a non-uniform magnetic field, only a torque acts on the dipole.
Reason: Force would also act on dipole if magnetic field were uniform .
Answer. D

Question. Assertion: The poles of magnet cannot be separated by breaking into two pieces.
Reason: The magnetic moment will be reduced to half when a magnet is broken into two equal pieces.
Answer. B

Question. Assertion: Magnetic moment of an atom is due to both, the orbital motion and spin motion of every electron.
Reason : All charged particles produce a magnetic field.
Answer. C

Question. Assertion: The coils of a spring come close to each other, when current is passed through it.
Reason: The coils of a spring carry current in the same direction and hence attract each other.
Answer. A

Question. Assertion: If an electron and proton enter a magnetic field with equal momentum, then the paths of both of them will be equally curved.
Reason: The magnitude of charge on an electron is same as that on a proton.
Answer. A

Question. Assertion: Magnetic field due to an infinite straight conductor varies inversely as the distance from it.
Reason: The magnetic field due to a straight conductor is in the form of concentric circles.
Answer. B

Question. Assertion: Force experienced by moving charge will be maximum if direction of velocity of charge is parallel to applied magnetic field.
Reason: Force on moving charge is independent of direction of applied magnetic field.
Answer. D

Question. Assertion : The magnetic field at the ends of a very long current carrying solenoid is half of that at the centre.
Reason : If the solenoid is sufficiently long, the field within it is uniform.
Answer. B

Question. Assertion : If the current in a solenoid is reversed in direction while keeping the same magnitude, the magnetic field energy stored in the solenoid remains unchanged.
Reason : Magnetic field energy density is proportional to the magnetic field.
Answer. C

Please refer to attached file for CBSE Class 12 Physics Magnetic Effects of Current Assignment.