Consider a thin metallic sheet perpendicular to the plane of the paper
moving with speed ‘v’ in a uniform magnetic field B going into the plane of the paper (See figure). If charge densities $$\sigma $$1 and $$\sigma $$2 are induced on the left and right surfaces, respectively, of the sheet then (ignore fringe effects) :
A galvanometer has a 50 division scale. Battery has no internal resistance. It is found that there is deflection of 40 divisions when R = 2400 $$\Omega $$. Deflection becomes 20 divisions when resistance taken from resistance box is 4900 $$\Omega $$. Then we can conclude :
Resistance of galvanometer is 200 $$\Omega $$
Full scale deflection current is 2 mA.
Current sensitivity of galvanometer is 20 $$\mu $$A/division.
Resistance required on R.B. for a deflection of 10 divisions is 9800 $$\Omega $$.
Let full scale deflection of current = I
In case 1, when R = 2400 $$\Omega $$ and deflection of 40 divisions present.
When a current of 5 mA is passed through a galvanometer having a coil of resistance 15$$\Omega $$, it shows full
scale deflection. The value of the resistance to be put in series with the galvanometer to convert it into a
voltmeter of range 0 – 10V is:
4.005 × 103 $$\Omega $$
1.985 × 103 $$\Omega $$
2.535 × 103 $$\Omega $$
2.045 × 103 $$\Omega $$
Given : Current through the galvanometer,
ig = 5 × 10–3 A
Galvanometer resistance, G = 15 $$\Omega $$
Let resistance R to be put in series with the galvanometer to
convert it into a voltmeter.
V = ig (R + G)
10 = 5 × 10–3 (R + 15)
$$ \therefore $$ R = 2000 – 15 = 1985
= 1.985 × 103 $$\Omega $$
MCQ (Single Correct Answer)
JEE Main 2017 (Offline)
A magnetic needle of magnetic moment 6.7 $$\times$$ 10-2 A m2 and moment of inertia 7.5 $$\times$$ 10-6 kg m2 is
performing simple harmonic oscillations in a magnetic field of 0.01 T. Time taken for 10 complete oscillations is: