All STD 12 -Electromagnetic induction questions
Newest firstShowing 101–150 of 151 questions
- 101. For the given circuit, comment on the type of transformer used:
2021 Medium - 102. For the given circuit the current \(i\) through the battery when the key in closed and the steady state has been reached is .....\(A\)
2021 Hard - 103. Four identical long solenoids \(A, B, C\) and \(D\) are connected to each other as shown in the figure. If the magnetic field at the center of \(A\) is \(3\, T\), the field at the center of \(C\) would be........... \(T\) (Assume that the magnetic field is confined with in the volume of respective solenoid).
2021 Hard - 104. In the given figure the magnetic flux through the loop increases according to the relation \(\phi_{B}(t)=10 t^{2}+20 t\), where \(\phi_{B}\) is in milliwebers and \(t\) is in seconds. The magnitude of current through \({R}=2 \,\Omega\) resistor at \({t}=5\, {s}\) is \(....\,{mA}\).
2021 Medium - 105. The arm \(P Q\) of a rectangular conductor is moving from \(x=0\) to \(x=2 b\) outwards and then inwards from \(x=2 b\) to \(x=0\) as shown in the figure. A uniform magnetic field perpendicular to the plane is acting from \(x=0\) to \(x=b\). Identify the graph showing the variation of different quantities with distance.
2021 Hard - 106. The current \((i)\) at time \(t =0\) and \(t =\infty\) respectively for the given circuit is
2021 Hard - 107. The magnetic field in a region is given by \(\overrightarrow{ B }= B _{0}\left(\frac{ x }{ a }\right) \,\hat{ k }\). A square loop of side \(d\) is placed with its edges along the \(x\) and \(y\) axes. The loop is moved with a constant velocity \(\overrightarrow{ v }= v _{0} \hat{ i }\). The emf induced in the loop is:
2021 Hard - 108. The time taken for the magnetic energy to reach \(25\, \%\) of its maximum value, when a solenoid of resistance \(R ,\) inductance \(L\) is connected to a battery, is : 2021 Hard
- 109. A circular coil of radius \(10\, cm\) is placed in a uniform magnetic field of \(3.0 \times 10^{-5}\, T\) with its plane perpendicular to the field initially. It is rotated at constant angular speed about an axis along the diameter of coil and perpendicular to magnetic field so that it undergoes half of rotation in \(0.2\,s.\) The maximum value of \(EMF\) induced (in \(\mu V\) ) in the coil will be close to the integer\(....\mu V\) 2020 Hard
- 110. A long solenoid of radius \(\mathrm{R}\) carries a time \((t)-\)dependent current \(\mathrm{I}(\mathrm{t})=\mathrm{I}_{0} \mathrm{t}(1-\mathrm{t})\). A ring of radius \(2 \mathrm{R}\) is placed coaxially near its middle. During the time interval \(0 \leq t \leq 1\), the induced current \(\left(\mathrm{I}_{\mathrm{R}}\right)\) and the induced \(\mathrm{EMF}\left(\mathrm{V}_{\mathrm{R}}\right)\) in the ring change as 2020 Hard
- 111. A loop \(ABCDEFA\) of straight edges has six corner points \(\mathrm{A}(0,0,0), \mathrm{B}(5,0,0),\)\(\mathrm{C}(5,5,0) ,\mathrm{D}(0,5,0), \mathrm{E}(0,5,5)\) and \(\mathrm{F}(0,0,5) .\) The magnetic field in this region is \(\overrightarrow{\mathrm{B}}=(3 \hat{\mathrm{i}}+4 \hat{\mathrm{k}}) \;\mathrm{T}\). The quantity of flux through the loop \(\mathrm{ABCDEFA}(\text { in Wb })\) is 2020 Medium
- 112. A part of a complete circuit is shown in the figure. At some instant, the value of current \(I\) is \(1\, A\) and it is decreasing at a rate of \(10^{2}\, A s ^{-1}\) The value of the potential difference \(V _{ P }- V _{ Q }\) (in volts) at that instant, is.
2020 Medium - 113. A planar loop made of wire is rotating in a uniform magnetic field. At time \(t=0\), the plane of the loop is perpendicular to the magnetic field. If the loop is rotating about an axis passing through its plane with a period of \(10\) seconds, at which of the following times will the induced electromotive force (emf) be maximum and minimum, respectively? 2020 Hard
- 114. A series \(L-R\) circuit is connected to a battery of emf \(V\). If the circuit is switched on at \(t =0\), then the time at which the energy stored in the inductor reaches \(\left(\frac{1}{n}\right)\) times of its maximum value, is 2020 Hard
- 115. A shown in the figure, a battery of \(emf \;\varepsilon\) is connected to an inductor \(L\) and resistance \(R\) in series. The switch is closed at \(t=0 .\) The total charge that flows from the battery, between \(\mathrm{t}=0\) and \(\mathrm{t}=\mathrm{t}_{\mathrm{c}}\;( \mathrm{t}_{\mathrm{c}}\) is the time constant of the circuit) is
2020 Hard - 116. A uniform magnetic field \(B\) exists in a direction perpendicular to the plane of a square loop made of a metal wire. The wire has a diameter of \(4\, mm\) and a total length of \(30\, cm\) The magnetic field changes with time at a steady rate \(dB / dt =0.032\, Ts ^{-1} .\) The induced current in the \(100 p\) is close to \(....A\) (Resistivity of the metal wire is \(\left.1.23 \times 10^{-8}\, \Omega m \right)\) 2020 Hard
- 117. An elliptical loop having resistance \(R\), of semi major axis \(a,\) and semi inor axis \(b\) is placed in a magnetic field as shown in the figure. If the loop is rotated about the \(x-\) axis with angular frequency \(\omega\), the average power loss in the loop due to Joule heating is :
2020 Hard - 118. An emf of \(20\; \mathrm{V}\) is applied at time \(\mathrm{t}=0\) to a circuit containing in series \(10\; \mathrm{mH}\) inductor and \(5 \;\Omega\) resistor. The ratio of the currents at time \(\mathrm{t}=\infty\) and at \(t=40\; s\) is close to : (Take \(e^{2}=7.389\) ) 2020 Medium
- 119. An infinitely long straight wire carrying current \(I,\) one side opened rectangular loop and a conductor \(C\) with a sliding connector are located in the same plane, as shown in the figure. The connector has length \(l\) and resistance \(R\). It slides to the right with a velocity \(V.\) The resistance of the conductor and the self inductance of the loop are negligible. The induced current in the loop, as a function of separation \(r,\) between the connector and the straight wire is
2020 Hard - 120. At time \(\mathrm{t}=0\) magnetic field of \(1000\) Gauss is passing perpendicularly through the area defined by the closed loop shown in the figure. If the magnetic field reduces linearly to \(500\) Gauss, in the next \(5 \;\mathrm{s}\), then induced \(EMF\) in the loop is ........\( \mu \mathrm{V}\)
2020 Medium - 121. Consider a circular coil of wire carrying constant current \(I\), forming a magnetic dipole. The magnetic flux through an infinite plane that contains the circular coil and excluding the circular coil area is given by \(\phi_{i} .\) The magnetic flux through the area of the circular coil area is given by \(\phi_{0} .\) Which of the following option is correct? 2020 Easy
- 122. In a fluorescent lamp choke (a small transformer) \(100 \;\mathrm{V}\) of reverse voltage is produced when the choke current changes uniformly from \(0.25 \;\mathrm{A}\) to \(0\;\mathrm{A}\) in a duration of \(0.025 \;\mathrm{ms} .\) The self-inductance of the choke (in \(\mathrm{mH})\) is estimated to be 2020 Medium
- 123. Two concentric circular coils, \(C _{1}\) and \(C _{2}\), are placed in the \(XY\) plane. \(C _{1}\) has \(500\) turns, and a radius of \(1\; cm . C _{2}\) has \(200\) turns and radius of \(20\, cm . C _{2}\) carries a time dependent current \(I(t)=\left(5 t^{2}-2 t+3\right) \;A\) where \(t\) is in \(s\). The \(emf\) nduced in \(C _{1}\) (in \(mV\) ), at the instant \(t =1\; s\) is \(\frac{4}{ x }\). The value of \(x\) is 2020 Medium
- 124. A \(10\,m\) long horizontal wire extends from North East to South West. It is falling with a speed of \(5.0\,ms^{-1},\) at right angles to the horizontal component of the earth’s magnetic field, of \(0.3\times 10^{-4}\,Wb/m^2\). The value of the induced \(emf\) in wire is 2019 Medium
- 125. A coil of self inductance \(10\,mH\) and resistance \(0.1\,\Omega \) is connected through a switch to a battery of internal resistance \(0.9\,\Omega \). After the switch is closed the time taken for the current to attain \(80\%\) of the saturation values is: [take \(ln\,5 = 1.6\) ] 2019 Hard
- 126. A conducting circular loop made of a thin wire, has area \(3.5 \times 10^{-3}\, m^2\) and resistance \(10\,\Omega \). It is placed perpendicular to a time dependent magnetic field \(B(t) = (0.4\,T)\, sin\, (50\, \pi t)\). The field is uniform in space. Then the net charge flowing through the loop during \(t = 0\, s\) and \(t = 10\, ms\) is close to.......\(mC\) 2019 Hard
- 127. A copper wire is wound on a wooden frame, whose shape is that of an equilateral triangle. If the linear dimension of each side of the frame is increased by a factor of \(3\), keeping the number of turns of the coil per unit length of the frame the same, then self inductance of the coil 2019 Hard
- 128. A power transmission line feeds input power at \(2300\,V\) to a step down transfonner with its primary windings having \(4000\) turns, giving the output power at \(230\,V.\) If the current in the primary of the transformer is \(5\,A,\) and its efficiency is \(90\%,\) the output current would be......\(A\) 2019 Medium
- 129. A solid metal cube of edge length \(2\, cm\) is moving in a positive \(y-\) direction at a constant speed of \(6\, m/s\). There is a uniform magnetic field of \(0.1\, T\) in the positive \(z-\) direction. The potential difference between the two faces of the cube perpendicular to the \(x-\) axis, is.....\(mV\) 2019 Medium
- 130. A thin strip \(10\, cm\) long is on a \(U\) shaped wire of negligible resistance and it is connected to a spring of spring constant \(0.5\,Nm^{-1}\) (see figure). The assembly is kept in a uniform magnetic field of \(0.1\, T\). If the strip is pulled from its equilibrium position and released, the number of oscillations it performs before its amplitude decreases by a factor of \(e\) is \(N\). If the mass of the strip is \(50\, grams\), its resistance \(10\,\Omega \) and air drag negligible, \(N\) will be close to
2019 Hard - 131. A transformer consisting of \(300\) turns in the primary and \(150\) turns in the secondary gives output power of \(2.2\, kW\). If the current in the secondary coils is \(10\, A\), then the input voltage and current in the primary coil are 2019 Medium
- 132. The figure shows a square loop \(L\) of side \(5\, cm\) which is connected to a network of resistances. The whole set up is moving towards right with a constant speed of \(1\, cms^{-1}\). At some instant, a part of \(L\) is in a uniform magnetic field of \(1\, T\), perpendicular to the plane of the loop. If the resistance of \(L\) is \(1.7\,\Omega \), the current in the loop at that instant will be close to.....\(\mu A\)
2019 Hard - 133. The self produced \(emf\) of a coil is \(25\,volts\). When the current in it is changed at uniform rate from \(10\,A\) to \(25\, A\) in \(1\,s\), the change in the energy of the inductance is......\(J\) 2019 Hard
- 134. The total number of turns and cross-section area in solenoid is fixed. However, its length \(L\) is varied by adjusting the separation between windings. The inductance of solenoid will be proportional to 2019 Hard
- 135. There are two long co -axial solenoids of same length \(l.\) The inner and outer coils have radii \(r_1\) and \(r_2\) and number of turns per unit length \(n_1\) and \(n_2\) respectively. The ratio of mutual inductance to the self -inductance of the inner -coil is 2019 Hard
- 136. Two coils \(P\) and \(Q\) are separated by some distance. When a current of \(3\, A\) flows through coil \(P\) a magnetic flux of \(10^{-3}\, Wb\) passes through \(Q\). No current is passed through \(Q\). When no current passes through \(P\) and a current of \(2\, A\) passes through \(Q\), the flux through \(P\) is 2019 Medium
- 137. A coil of cross-sectional area \(A\) having \(n\) turns is placed in a uniform magnetic field \(B.\) When it is rotated with an angular velocity \(\omega ,\) the maximum \(e.m.f.\) induced in the coil will be 2018 Medium
- 138. A copper rod of mass \(m\) slides under gravity on two smooth parallel rails, with separation \(l\) and set at an angle of \(\theta\) with the horizontal. At the bottom, rails are joined by a resistance \(R\). There is a uniform magnetic field \(B\) normal to the plane of the rails, as shown in the figure. The terminal speed of the copper rod is
2018 Hard - 139. An ideal capacitor of capacitance \(0.2\, μF\) is charged to a potential difference of \(10\,V\). The charging battery is then disconnected. The capacitor is then connected to an ideal inductor of self inductance \(0.5\,mH\). The current at a time when the potential difference across the capacitor is \(5\,V\), is.....\(A\) 2018 Hard
- 140. At the centre of a fixed large circular coil of radius \(R\), a much smaller circular coil of radius \(r\) is placed. The two coils are concentric and are in the same plane. The larger coil carries a current \(I\). The smaller coil is set to rotate with a constant angular velocity \(\omega \) about an axis along their common diameter. Calculate the \(emf\) induced in the smaller coil after a time \(t\) of its start of rotation 2018 Hard
- 141. A small circular loop of wire of radius \(a\) is located at the centre of a much larger circular wire loop of radius \(b\). The two loops are in the same plane. The outer loop of radius \(b\) carries an alternating current \(I = I_0\, cos\, (\omega t)\) . The emf induced in the smaller inner loop is nearly 2017 Hard
- 142. In a coil of resistance \(100\ \Omega\) , a current is induced by changing the magnetic flux through it as shown in the figure. The magnitude of change in flux through the coil is......\(Wb\)
2017 Medium - 143. A conducting metal circular-wire-loop of radius \(r\) is placed perpendicular to a magnetic field which varies with time as \(B = {B_0}{e^{\frac{{ - t}}{\tau }}}\) , where \(B_0\) and \(\tau \) are constants, at time \(t = 0\). If the resistance of the loop is \(R\) then the heat generated in the loop after a long time \(\left( {t \to \infty } \right)\) is 2016 Hard
- 144. An inductor \((L = 0.03\;H)\) and a resistor \((R = 0.15 k\Omega )\) are connected in series to a battery of \(15\;V\) \(EMF\) in a circuit shown below. The key \(K_1\) has been kept closed for a long time. Then at \(t = 0\), \(K_1\) is opened and key \(K_2\) is closed simultaneously. At \(t = 1 \;ms\), the current in the circuit will be ........... \(mA\). (\({e^5} \cong 150)\)
2015 Hard - 145. When current in a coil changes from \(5\,A\) to \(2\,A\) in \(0 .1\,s,\) average voltage of \(50\,V\) is produced. The self- inductance of the coil is.......\(H\) 2015 Medium
- 146. A coil of circular cross-section having \(1000\, turns\) and \(4\, cm^2\) face area is placed with its axis parallel to a magnetic field which decreases by \(10^{-2}\, Wb\, m^{-2}\) in \(0.01\, s\). The \(e.m.f.\) induced in the coil is....\(mV\) 2014 Medium
- 147. A square frame of side \(10\, cm\) and a long straight wire carrying current \(1\, A\) are in the plate of the paper. Starting from close to the wire, the frame moves towards the right with a constant speed of \(10\, ms^{-1}\) (see figure). The \(e.m. f\) induced at the time the left arm of the frame is at \(x\, = 10\, cm\) from the wire is .....\(\mu V\)
2014 Medium - 148. In the circuit shown here, the point '\(C\)' is kept connected to point '\(A\)' till the current flowing through the circuit becomes constant. Afterward, suddenly, point '\(C\)' is disconnected from point '\(A\)' and connected to point '\(B\)' at time \(t = 0\). Ratio of the voltage across resistance and the inductor at \(t = L/R\) will be equal to:
2014 Medium - 149. A circular loop ofradius \(0.3\ cm\) lies parallel to amuch bigger circular loop ofradius \(20\ cm\). The centre of the small loop is on the axis of the bigger loop. The distance between their centres is \(15\ cm\). If a current of \(2.0\ A\) flows through the smaller loop, then the flux linked with bigger loop is 2013 Medium
- 150. A metallic rod oflength '\(l\)' is tied to a string oflength \(2l\). and made to rotate with angular speed w on a horizontal table with one end of the string fixed. Ifthere is a vertical magnetic field '\(B\)' in the region, the \(e.m.f.\) induced across the ends of the rod is
2013 Medium
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