Practice Questions

Q25.The image of an illuminated square is obtained on a screen with the help of a converging lens. The distance of the square from the lens is 40 cm. The area of the image is 9 times that of the square. The focal length of the lens is : (1) 36 cm (2) 27 cm (3) 60 cm (4) 30 cm

Q25. n identical waves each of intensity I0 interfere with each other. The ratio of maximum intensities if the interference is (i) coherent and (ii) incoherent is : (1) n2 (2) n1 (3) 1 (4) n n2

Q26.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: Short wave transmission is achieved due to the total internal reflection of the e-m wave from an appropriate height in the ionosphere. Statement-2: Refractive index of a plasma is independent of the frequency of e-m waves. (1) Statement-1 is true, Statement- 2 is false. (2) Statement-1 is false, Statement- 2 is true. (3) Statement-1 is true, Statement- 2 is true but (4) Statement-1 is true, Statement-2 is true and Statement −2 is not the correct explanation of Statement −2 is the correct explanation of statement-1. Statement-1.

Q26.In an experiment on photoelectric effect, a student plots stopping potential V0 against reciprocal of the wavelength λ of the incident light for two different metals A and B. These are shown in the figure. JEE Main 2013 (25 Apr Online) JEE Main Previous Year Paper Looking at the graphs, you can most appropriately say that: (1) Work function of metal B is greater than that of (2) For light of certain wavelength falling on both metal A metal, maximum kinetic energy of electrons emitted from A will be greater than those emitted from B. (3) Work function of metal A is greater than that of (4) Students data is not correct metal B

Q26.A person lives in a high-rise building on the bank of a river 50 m wide. Across the river is a well lit tower of height 40 m. When the person, who is at a height of 10 m, looks through a polarizer at an appropriate angle at light of the tower reflecting from the river surface, he notes that intensity of light coming from distance X from his building is the least and this corresponds to the light coming from light bulbs at height ' Y ' on the tower. The values of X and Y are respectively close to (refractive index of water ≃43 ) (1) 25 m, 10 m (2) 13 m, 27 m (3) 22 m, 13 m (4) 17 m, 20 m

Q26.Electrons are accelerated through a potential difference V and protons are accelerated through a potential difference 4 V. The de-Broglie wavelengths are λe and λp for electrons and protons respectively. The ratio of λe is given by: (given me is mass of electron and mp is mass of proton). λp (1) = λp λe = √mpme (2) λpλe √memp (3) = λp λe = 12 √memp (4) λpλe 2√mpme

Q27.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: In Young's double slit experiment, the number of fringes observed in the field of view is small with longer wavelength of light and is large with shorter wavelength of light. Statement-2: In the double slit experiment the fringe width depends directly on the wavelength of light. (1) Statement-1 is true, Statement-2 is true and the (2) Statement-1 is false and the Statement-2 is true. Statement-2 is correct explanation of the Statement-1. (3) Statement-1 is true Statement-2 is true and the (4) Statement-1 is true and the Statement-2 is false. Statement-2 is not correct explanation of the Statement-1.

Q27.The anode voltage of a photocell is kept fixed. The wavelength λ of the light falling on the cathode is gradually changed. The plate current I of the photocell varies as follows : (1) (2) (3) (4)

Q27.In the Bohr model an electron moves in a circular orbit around the proton. Considering the orbiting electron to be a circular current loop, the magnetic moment of the hydrogen atom, when the electron is in nth excited state, is : m e ) nh2π (1) ( 2me n2h2π ) (2) ( (3) ( 2me ) nh2π (4) ( me ) n2h2π JEE Main 2013 (09 Apr Online) JEE Main Previous Year Paper

Q28.In a hydrogen like atom electron makes transition from an energy level with quantum number n to another with quantum number (n −1). If n >> 1, the frequency of radiation emitted is proportional to : (1) 1 (2) 1 n3/2 n3 (3) 1 (4) 1 n n2

Q28.A system of four gates is set up as shown. The 'truth table' corresponding to this system is : (1) (2) (3) (4)

Q28.A 12.5eV electron beam is used to bombard gaseous hydrogen at room temperature. It will emit: (1) 2 lines in the Lyman series and 1 line in the (2) 3 lines in the Lyman series Balmar series (3) 1 line in the Lyman series and 2 lines in the (4) 3 lines in the Balmer series Balmar series

Q29.Consider two npn transistors as shown in figure. If 0 Volts corresponds to false and 5 Volts correspond to true then the output at C corresponds to : (1) A NAND B (2) A OR B (3) AAND B (4) ANOR B

Q29.Which of the following statement is NOT correct? (1) Ground wave signals are more stable than the sky (2) The critical frequency of an ionospheric layer is wave signals. the highest frequency that will be reflected back by the layer when it is vertically incident. (3) Electromagnetic waves of frequencies higher (4) Sky wave signals in the broadcast frequency than about 30MHz cannot penetrate the range are stronger at night than in the day time. ionosphere.

Q29.A diode detector is used to detect an amplitude modulated wave of 60% modulation by using a condenser of capacity 250 pico farad in parallel with a load resistance of 100 kilo ohm. Find the maximum modulated frequency which could be detected by it. (1) 5.31 MHz (2) 5.31 kHz (3) 10.62 MHz (4) 10.62 kHz

Q29. Which of the following circuits correctly represents the following truth table ? (1) (2) (3) (4) JEE Main 2013 (25 Apr Online) JEE Main Previous Year Paper

Q29.The half-life of a radioactive element A is the same as the mean-life of another radioactive element B. Initially both substances have the same number of atoms, then : (1) A and B decay at the same rate always. (2) A and B decay at the same rate initially. (3) A will decay at a faster rate than B. (4) B will decay at a faster rate than A .

Q30.Figure shows a circuit in which three identical diodes are used. Each diode has forward resistance of 20Ω and infinite backward resistance. Resistors R1 = R2 = R3 = 50Ω. Battery voltage is 6 V . The current through R3 is : (1) 50 mA (2) 100 mA (3) 60 mA (4) 25 mA

Q31.The density of 3M solution of sodium chloride is 1.252 g mL−1 . The molality of the solution will be : ( molar mass, NaCl = 585 g mol−1) (1) 260 m (2) 2.18 m (3) 2.79 m (4) 3.00 m

Q32.Electron gain enthalpy with negative sign of fluorine is less than that of chlorine due to : (1) High ionization enthalpy of fluorine (2) Smaller size of chlorine atom (3) Smaller size of fluorine atom (4) Bigger size of 2p orbital of fluorine

Q32.How many grams of methyl alcohol should be added to 10 litre tank of water to prevent its freezing at 268 K ? ( Kf for water is 1.86 K kg mol−1) (1) 880.07 g (2) 899.04 g (3) 886.02 g (4) 868.06 g Q33. 10 mL of 2(M) NaOH solution is added to 200 mL of 0.5 (M) of NaOH solution. What is the final concentration ? (1) 0.57(M) (2) 5.7(M) (3) 11.4(M) (4) 1.14(M)

Q32.How many litres of water must be added to 1 litre of aqueous solution of HCl with a pH of 1 to create an aqueous solution with pH of 2 ? (1) 2. 0 (2) 9. 0 (3) 0. 1 (4) 0. 9

Q33.Which is the correct order of second ionization potential of C, N, O and F in the following ? (1) O > N > F > C (2) O > F > N > C (3) F > O > N > C (4) C > N > O > F

Q33.Experimentally it was found that a metal oxide has formula M0.98O. Metal M, is present as M2+ and M3+ in its oxide. Fraction of the metal which exists as M3+ would be: (1) 6. 05% (2) 5. 08% (3) 7. 01% (4) 4. 08%

Q33.Which one of the following molecules is polar? (1) XeF4 (2) IF5 (3) SbF5 (4) CF4