1
JEE Main 2018 (Offline)
MCQ (Single Correct Answer)
+4
-1
Change Language
The dipole moment of a circular loop carrying a current I, is m and the magnetic field at the centre of the loop is B1. When the dipole moment is doubled by keeping the current constant, the magnetic field at the centre of the loop is $${{B_2}}$$. The ratio $${{{B_1}} \over {{B_2}}}$$ is:
A
2
B
$$\sqrt 3 $$
C
$$\sqrt 2 $$
D
$$1 \over \sqrt 2 $$
2
JEE Main 2018 (Offline)
MCQ (Single Correct Answer)
+4
-1
Change Language
In an a.c. circuit, the instantaneous e.m.f. and current are given by
e = 100 sin 30 t
i = 20 sin $$\left( {30t - {\pi \over 4}} \right)$$
In one cycle of a.c., the average power consumed by the circuit and the wattless current are, respectively
A
50, 0
B
50, 10
C
$${{1000} \over {\sqrt 2 }},10$$
D
$${{50} \over {\sqrt 2 }}$$
3
JEE Main 2018 (Offline)
MCQ (Single Correct Answer)
+4
-1
Out of Syllabus
Change Language
For an RLC circuit driven with voltage of amplitude vm and frequency $${\omega _0}$$ = $${1 \over {\sqrt {LC} }}$$ the current exhibits resonance. The quality factor, Q is given by :
A
$${{CR} \over {{\omega _0}}}$$
B
$${{{\omega _0}L} \over R}$$
C
$${{{\omega _0}R} \over L}$$
D
$${R \over {\left( {{\omega _0}C} \right)}}$$
4
JEE Main 2018 (Offline)
MCQ (Single Correct Answer)
+4
-1
Change Language
An EM wave from air enters a medium. The electric fields are

$$\overrightarrow {{E_1}} $$ = $${E_{01}}\widehat x\cos \left[ {2\pi v\left( {{z \over c} - t} \right)} \right]$$ in air and

$$\overrightarrow {{E_2}} $$ = $${E_{02}}\widehat x\cos \left[ {k\left( {2z - ct} \right)} \right]$$ in medium,

where the wave number k and frequency $$\nu $$ refer to their values in air. The medium is non-magnetic. If $${\varepsilon _{{r_1}}}$$ and $${\varepsilon _{{r_2}}}$$ refer to relative permittivities of air and medium respectively, which of the following options is correct ?
A
$${{{\varepsilon _{{r_1}}}} \over {{\varepsilon _{{r_2}}}}} = 4$$
B
$${{{\varepsilon _{{r_1}}}} \over {{\varepsilon _{{r_2}}}}} = 2$$
C
$${{{\varepsilon _{{r_1}}}} \over {{\varepsilon _{{r_2}}}}} = {1 \over 4}$$
D
$${{{\varepsilon _{{r_1}}}} \over {{\varepsilon _{{r_2}}}}} = {1 \over 2}$$
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