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question_answer1) A hypothetical atom has only three energy levels. The ground level has energy, \[{{E}_{1}}=-8eV.\]The two excited states have energies, \[{{E}_{2}}=-6eV\]and\[{{E}_{3}}=-2eV.\]Then which of the following wavelengths will not be present in the emission spectrum of this atom?
JEE Main Online Paper (Held On 12 May 2012)
A)
207 nm
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B)
465 nm
done
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C)
310 nm
done
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D)
620 nm
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question_answer2) A given ideal gas with \[\gamma =\frac{{{C}_{p}}}{{{C}_{v}}}=1.5\]at a temperature T. If the gas is compressed adiabatically to one-fourth of its initial volume, the final temperature will be
JEE Main Online Paper (Held On 12 May 2012)
A)
\[2\sqrt{2}T\]
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B)
4 T
done
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C)
2 T
done
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D)
8 T
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question_answer3) A resistance R and a capacitance C are connected in series to a battery of negligible internal resistance through a key. The key is closed at t = If after t sec the voltage across the capacitance was seven times the voltage across R, the value of t is
JEE Main Online Paper (Held On 12 May 2012)
A)
\[3RC\ell n2\]
done
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B)
\[2RC\,\ell n2\]
done
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C)
\[2RC\,\ell n7\]
done
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D)
\[3RC\,\ell n7\]
done
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question_answer4) The magnetic force acting on charged particle of charge \[2\mu C\]in magnetic field of 2 F acting in y-direction, when the particle velocity is \[\left( 2\hat{i}+3\hat{j} \right)\times {{10}^{6}}m{{s}^{-1}}\]is
JEE Main Online Paper (Held On 12 May 2012)
A)
8 N in z-direction
done
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B)
8 N in y-direction
done
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C)
4 N in y-direction
done
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D)
4 N in z-direction
done
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question_answer5) This question has Statement 1 and Statement 2. Of the four choices given after the Statements, choose the one that best describes the two Statements. Statement 1: A pure semiconductor has negative temperature coefficient of resistance. Statement 2: On raising the temperature, more charge carriers are released into the conduction band.
JEE Main Online Paper (Held On 12 May 2012)
A)
Statement 1 is false. Statement 2 is true.
done
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B)
Statement 1 is true. Statement 2 is false.
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C)
Statement 1 is true. Statement 2 is true, Statement 2 is not a correct explanation of Statement 1.
done
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D)
Statement 1 is true. Statement 2 is true, Statement 2 is the correct explanation of Statement 1.
done
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question_answer6) A projectile moving vertically upwards with a velocity of 200 \[\text{m}{{\text{s}}^{-1}}\]breaks into two equal parts at a height of 490 m. One part starts moving vertically upwards with a velocity of 400 \[\text{m}{{\text{s}}^{-1}}\]. How much time it will take, after the break up with the other part to hit the ground?
JEE Main Online Paper (Held On 12 May 2012)
A)
\[2\sqrt{10}s\]
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B)
5 s
done
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C)
10 s
done
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D)
\[\sqrt{10}s\]
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question_answer7)
n moles of an ideal gas undergo a process \[A\to B\]as shown in the figure. Maximum temperature of the gas during the process is
JEE Main Online Paper (Held On 12 May 2012)
A)
\[\frac{8{{P}_{0}}{{V}_{0}}}{nR}\]
done
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B)
\[\frac{3{{P}_{0}}{{V}_{0}}}{2nR}\]
done
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C)
\[\frac{9{{P}_{0}}{{V}_{0}}}{2nR}\]
done
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D)
\[\frac{9{{P}_{0}}{{V}_{0}}}{4nR}\]
done
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question_answer8) A student measured the diameter of a wire using a screw gauge with the least count 0.001 cm and listed the measurements. The measured value should be recorded as
JEE Main Online Paper (Held On 12 May 2012)
A)
5.3200cm
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B)
5.3cm
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C)
5.32cm
done
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D)
5.320cm
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question_answer9) The first diffraction minimum due to the single slit diffraction is seen at \[\theta ={{30}^{o}}\]for a light of wavelength \[5000\overset{\text{o}}{\mathop{\text{A}}}\,\] falling perpendicularly on the slit. The width of the slit is
JEE Main Online Paper (Held On 12 May 2012)
A)
\[2.5\times {{10}^{-5}}cm\]
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B)
\[1.25\times {{10}^{-5}}cm\]
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C)
\[10\times {{10}^{-5}}cm\]
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D)
\[5\times {{10}^{-5}}cm\]
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question_answer10) This question has Statement 1 and Statement 2. Of the four choices given after the Statements, choose the one that best describes the two Statements. Statement 1: Bats emitting ultrasonic waves can detect the location of a prey by hearing the waves reflected from it. Statement 2: When the source and the detector are moving, the frequency of reflected waves is changed.
JEE Main Online Paper (Held On 12 May 2012)
A)
Statement 1 is false. Statement 2 is true.
done
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B)
Statement 1 is true, Statement 2 is false.
done
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C)
Statement 1 is true. Statement 2 is true, Statement 2 is not the correct explanation of Statement 1.
done
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D)
Statement 1 is true. Statement 2 is true, Statement 2 is the correct explanation of Statement 1.
done
clear
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question_answer11) Assuming the earth to be a sphere of uniform density, the acceleration due to gravity inside the earth at a distance of r from the centre is proportional to
JEE Main Online Paper (Held On 12 May 2012)
A)
r
done
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B)
\[{{r}^{-1}}\]
done
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C)
\[{{r}^{2}}\]
done
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D)
\[{{r}^{-2}}\]
done
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question_answer12) A doubly ionised Li atom is excited from its ground state (n=1) to n=3 state. The wavelengths of the spectral lines are given by \[{{\lambda }_{32}},{{\lambda }_{31}}\]and\[{{\lambda }_{21}}.\]The ratio \[{{\lambda }_{32}}/{{\lambda }_{31}}\]and\[{{\lambda }_{21}}/{{\lambda }_{31}}\]are, respectively
JEE Main Online Paper (Held On 12 May 2012)
A)
8.1,0.67
done
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B)
8.1,1.2
done
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C)
6.4,1.2
done
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D)
6.4,0.67
done
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question_answer13) Which of the following Statements is correct?
JEE Main Online Paper (Held On 12 May 2012)
A)
The rate of radioactive decay cannot be controlled but that of nuclear fission can be controlled.
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B)
Nuclear forces are short range, attractive and charge dependent.
done
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C)
Nuclei of atoms having same number of neutrons are known as isobars.
done
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D)
Wavelength of matter waves is given by de Broglie formula but that of photons is not given by the same formula d. Nuclear fission can be controlled but not of nuclear fusion.
done
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question_answer14) The distance travelled by a body moving along a line in time / is proportional to t3. The acceleration-time (a,t) graph for the motion of the body will be
JEE Main Online Paper (Held On 12 May 2012)
A)
done
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B)
done
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C)
done
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D)
done
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question_answer15) A wave represented by the equation \[{{y}_{1}}=a\cos (kx-\omega t)\]is superimposed with another wave to form a stationary wave such that the point x ? 0 is node. The equation for the other wave is
JEE Main Online Paper (Held On 12 May 2012)
A)
\[a\cos (kx-\omega t+\pi )\]
done
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B)
\[a\cos (kx-\omega t+\pi )\]
done
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C)
\[a\cos \left( kx+\omega t+\frac{\pi }{2} \right)\]
done
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D)
\[a\cos \left( kx-\omega t+\frac{\pi }{2} \right)\]
done
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question_answer16)
An insect crawls up a hemispherical surface very slowly. The coefficient of friction between the insect and the surface is 1/3. If the line joining the centre of the hemispherical surface to the insect makes an angle a with the vertical, the maximum possible value of a so that the insect does not slip is given by
JEE Main Online Paper (Held On 12 May 2012)
A)
\[\cot \alpha =3\]
done
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B)
\[\sec \alpha =3\]
done
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C)
\[\cos ec\,\alpha =3\]
done
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D)
\[\cos \,\alpha =3\]
done
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question_answer17) Water is flowing through a horizontal tube having cross-sectional areas of its two ends being A and A' such that the ratio A/A' is 5. If the pressure difference of water between the two ends is \[3\times {{10}^{5}}N{{m}^{-2}},\] the velocity of water with which it enters the tube will be (neglect gravity effects)
JEE Main Online Paper (Held On 12 May 2012)
A)
\[5\,m\,{{s}^{-1}}\]
done
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B)
\[10\,m\,{{s}^{-1}}\]
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C)
\[25\,m\,{{s}^{-1}}\]
done
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D)
\[50\sqrt{10}\,m\,{{s}^{-1}}\]
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question_answer18)
A solid sphere is rolling on a surface as shown in figure, with a translational velocity \[v\,m\,{{s}^{-1}}.\] If it is to climb the inclined surface continuing to roll without slipping, then minimum velocity for this to happen is
JEE Main Online Paper (Held On 12 May 2012)
A)
\[\sqrt{2gh}\]
done
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B)
\[\sqrt{\frac{7}{5}gh}\]
done
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C)
\[\sqrt{\frac{7}{2}gh}\]
done
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D)
\[\sqrt{\frac{10}{7}gh}\]
done
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question_answer19) Three resistors of \[4\Omega ,6\Omega \]and \[12\Omega \]are connected in parallel and the combination is connected in series with a 1.5 V battery of\[1\Omega \]internal resistance. The rate of Joule heating in the \[4\Omega \]resistor is
JEE Main Online Paper (Held On 12 May 2012)
A)
0.55W
done
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B)
0.33 W
done
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C)
0.25 W
done
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D)
0.86 W
done
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question_answer20) We wish to make a microscope with the help of two positive lenses both with a focal length of 20 mm each and the object is positioned 25 mm from the objective lens. How far apart the lenses should be so that the final image is formed at infinity?
JEE Main Online Paper (Held On 12 May 2012)
A)
20mm
done
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B)
100mm
done
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C)
120mm
done
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D)
80mm
done
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question_answer21)
Magnetic flux through a coil of resistance \[10\Omega \]is changed by \[\Delta \phi \]in 0.1 s. The resulting current in the coil varies with time as shown in the figure. Then\[|\Delta \phi |\]is equal to (in weber)
JEE Main Online Paper (Held On 12 May 2012)
A)
6
done
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B)
4
done
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C)
2
done
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D)
8
done
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question_answer22) A series combination of\[{{n}_{1}}\] capacitors, each of capacity \[{{C}_{1}}\] is charged by source of potential difference 4 V. When another parallel combination of \[{{n}_{2}}\]capacitors each of capacity \[{{C}_{2}}\] is charged by a source of potential difference V, it has the same total energy stored in it as the first combination has. The value of \[{{C}_{2}}\] in terms of \[{{C}_{1}}\]is then
JEE Main Online Paper (Held On 12 May 2012)
A)
\[16\frac{{{n}_{2}}}{{{n}_{1}}}{{C}_{1}}\]
done
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B)
\[\frac{2{{C}_{1}}}{{{n}_{1}}{{n}_{2}}}\]
done
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C)
\[2\frac{{{n}_{2}}}{{{n}_{1}}}{{C}_{1}}\]
done
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D)
\[\frac{16{{C}_{1}}}{{{n}_{1}}{{n}_{2}}}\]
done
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question_answer23) It is preferable to measure the e.m.f. of a cell by potentiometer than by a voltmeter because of the following possible reasons. (i) In case of potentiometer, no current flows through the cell. (ii) The length of the potentiometer allows greater precision. (iii) Measurement by the potentiometer is quicker. (iv) The sensitivity of the galvanometer, when using a potentiometer is not relevant. Which of these reasons are correct?
JEE Main Online Paper (Held On 12 May 2012)
A)
(i),(iii),(iv)
done
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B)
(i), (iii), (iv)
done
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C)
(i),(ii)
done
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D)
(i),(ii),(iii),(iv)
done
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question_answer24) Two bodies A and B of mass m and 2m respectively are placed on a smooth floor. They are connected by a spring of negligible mass. A' third body C of mass m is placed on the floor. The body C moves with a velocity \[{{v}_{0}}\] along the line joining A and B and collides elastically with A. At a certain time after the collision it is found that the instantaneous velocities of A and B are same and the compression of the spring is \[{{x}_{0}}\]. The spring constant k will be
JEE Main Online Paper (Held On 12 May 2012)
A)
\[m\frac{v_{0}^{2}}{x_{0}^{2}}\]
done
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B)
\[m\frac{{{v}_{0}}}{2{{x}_{0}}}\]
done
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C)
\[2m\frac{{{v}_{0}}}{{{x}_{0}}}\]
done
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D)
\[\frac{2}{3}m{{\left( \frac{{{v}_{0}}}{{{x}_{0}}} \right)}^{2}}\]
done
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question_answer25)
The circuit in figure consists of wires at the top and bottom and identical springs as the left and right sides. The wire at the bottom has a mass of 10 g and is 5 cm long. The wire is hanging as shown in the figure. The springs stretch 0.5 cm under the weight of the wire and the circuit has a, total resistance of \[12\Omega .\] When the lower wire is subjected to a static magnetic field, the springs, stretch an additional 0.3 cm. The magnetic field is
JEE Main Online Paper (Held On 12 May 2012)
A)
0.6 T and directed out of page
done
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B)
1.2 T and directed into the plane of page
done
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C)
0.6 T and directed into the plane of page
done
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D)
1.2 T and directed out of page
done
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question_answer26) In a sensitive meter bridge apparatus the bridge wire should possess
JEE Main Online Paper (Held On 12 May 2012)
A)
high resistivity and low temperature coefficient.
done
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B)
low resistivity and high temperature coefficient.
done
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C)
low resistivity and low temperature coefficient.
done
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D)
high resistivity and high temperature coefficient.
done
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question_answer27)
A spring is compressed between two blocks of masses \[{{m}_{1}}\] and \[{{m}_{2}}\] placed on a horizontal frictionless surface as shown in the figure. When the blocks are released, they have initial velocity of \[{{v}_{1}}\] and \[{{v}_{2}}\] as shown. The blocks travel distances \[{{x}_{1}}\] and \[{{x}_{2}}\] respectively before coming to rest. The ratio \[\left( \frac{{{x}_{1}}}{{{x}_{2}}} \right)\] is
JEE Main Online Paper (Held On 12 May 2012)
A)
\[\frac{{{m}_{2}}}{{{m}_{1}}}\]
done
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B)
\[\frac{{{m}_{1}}}{{{m}_{2}}}\]
done
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C)
\[\sqrt{\frac{{{m}_{2}}}{{{m}_{1}}}}\]
done
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D)
\[\sqrt{\frac{{{m}_{1}}}{{{m}_{2}}}}\]
done
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question_answer28) This question has Statement land Statement 2. Of the four choices given after the Statements, choose the one that best describes the two Statements. Statement 1: When moment of inertia/of a body rotating about an axis with angular speed \[\omega \]increases, its angular momentum L is unchanged but the kinetic energy K increases if there is no torque applied on it. Statement 2: \[L=I\omega ,\] kinetic energy of rotation \[=\frac{1}{2}I{{\omega }^{2}}\]
JEE Main Online Paper (Held On 12 May 2012)
A)
(a) Statement 1 is true, Statement 2 is true, Statement 2 is not the correct explanation of Statement 1.
done
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B)
(b) Statement 1 is false, Statement 2 is true.
done
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C)
(c) Statement 1 is true, Statement 2 is true. Statement 2 is correct explanation of the Statement 1.
done
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D)
(d) Statement 1 is true, Statement 2 is false.
done
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question_answer29) A 10 kW transmitter emits radio waves of wavelength 500 m. The number of photons emitted per second by the transmitter is of the order of
JEE Main Online Paper (Held On 12 May 2012)
A)
1037
done
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B)
1031
done
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C)
1025
done
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D)
1043
done
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question_answer30) The maximum number of possible interference maxima for slit separation equal to 1. 8A,, where X is the wavelength of light used, in a Young's double slit experiment is
JEE Main Online Paper (Held On 12 May 2012)
A)
zero
done
clear
B)
3
done
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C)
infinite
done
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D)
5
done
clear
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