Practice Questions

Q28.In the figure, given that VBB supply can vary from 0 to 5.0 V , VCC = 5 V , βdc = 200, RB = 100 kΩ, RC = 1 kΩ and VBE = 1.0V. The minimum base current and the input voltage at which the transistor will go to saturation, will be, respectively: (1) 25 μA and 2.8 V (2) 20μA and 2.8V (3) 25μA and 3.5V (4) 20μA and 3.5V

Q28.Taking the wavelength of first Balmer line in hydrogen spectrum (n = 3 to n = 2) as 660 nm , the wavelength of the 2nd Balmer line (n = 4 to n = 2) will be : (1) 889.2 nm (2) 488.9 nm (3) 388.9 nm (4) 642.7 nm

Q28.The circuit shown below contains two ideal diodes, each with a forward resistance of 50Ω. If the battery voltage is 6 V, the current through the 100Ω resistance (in Amperes) is: (1) 0.036 (2) 0.02 (3) 0.027 (4) 0.03

Q28.Figure shows a DC voltage regulator circuit, with a Zener diode of breakdown voltage = 6 V . If the unregulated input voltage varies between 10 V to 16 V, then what is the maximum Zener current? (1) 1.5 mA (2) 3.5 mA (3) 7.5 mA (4) 2.5 mA

Q28.Consider the nuclear fission, Ne20 →2 He4 + C12 . Given that the binding energy/nucleon of Ne20, He4 and C12 are 8.03 MeV, 7.86 MeV , respectively. Identify the correct statement: (1) Energy of 12. 4 MeV will be supplied. (2) Energy of 9. 72 MeV has to be supplied. (3) Energy of 3. 6 MeV will be released. (4) 8. 3 MeV energy will be released.

Q29.A message signal of frequency 100 MHz and peak voltage 100 V is used execute amplitude modulation on a carrier wave of frequency 300 GHz and peak voltage 400 V . The modulation index and difference between the two side band frequencies are: (1) 4; 2 × 108 Hz (2) 0.25; 2 × 108 Hz (3) 4; 1 × 108 Hz (4) 0.25; 1 × 108 Hz

Q29.An amplitude modulated signal is given by V(t) = 10[1 + 0.3 cos (2.2 × 104t)] sin (5.5 × 105t). Here t is in seconds. The sideband frequencies (in kHz ) are, [Given π = 22/7 ] (1) 1785 and 1715 (2) 178.5 and 171.5 (3) 89.25 and 85.75 (4) 892.5 and 857.5

Q29.For the circuit shown below, the current through the Zener diode is (1) zero. (2) 5 mA . (3) 9 mA . (4) 14 mA . JEE Main 2019 (10 Jan Shift 2) JEE Main Previous Year Paper

Q29.A TV transmission tower has a height of 140 m and the height of the receiving antenna is 40 m. What is the maximum distance upto which signals can be broadcasted from this tower in LOS (Line of Sight) mode? (Given: radius of earth = 6.4 × 106 m). (1) 48 km (2) 40 km (3) 80 km (4) 65 km

Q29.Two radioactive substances A and B have decay constants 5λ and λ respectively. At t = 0, a sample has the 1 2 same number of the two nuclei. The time taken for the ratio of the number of nuclei to become will be e 1 1 (1) (2) λ 2λ 2 1 (3) (4) λ 4λ

Q29.The surface of certain metal is first illuminated with light of wavelength 𝜆1 = 350 nm and then, by a light of wavelength 𝜆2 = 540 nm . It is found that the maximum speed of the photoelectrons in the two cases differ by a factor of 2. The work function of the metal (in eV) is close to 1240 (Energy of photon = eV ) 𝜆in nm (1) 2.5 (2) 1.8 (3) 5.6 (4) 1.4

Q29.The reverse break down voltage of a Zener diode is 5.6 V in the given circuit. The current I𝑧 through the Zener is: (1) 10 mA (2) 7 mA (3) 17 mA (4) 15 mA

Q29.A common emitter amplifier circuit, built using an NPN transistor, is shown in the figure. Its dc current gain is 250, 𝑅𝐶= 1 kΩ and 𝑉𝐶𝐶= 10 V . The minimum base current for VCE to reach saturation is (1) 10 μA (2) 40 μA (3) 7 μA (4) 100 μA

Q29.The logic gate equivalent to the given logic circuit is: (1) NAND (2) AND (3) NOR (4) OR

Q29. An amplitude modulated signal is plotted below: Which one of the following best describes the above signal? (1) (9 + sin (2.5π × 105t)) sin (2π × 104t)V (2) (1 + 9 sin (2π × 104t)) sin (2.5π × 105t)V (3) (9 + sin (2π × 104t)) sin (2.5π × 105t)V (4) (9 + sin (4π × 104t)) sin (5π × 105t)V

Q29.In a communication system operating at wavelength 800 nm, only one percent of source frequency is available as signal bandwidth. The number of channels accommodated for transmitting TV signals of band width 6 MHz are (Take velocity of light c = 3 × 108 m/s, h = 6.6 × 10−34 J-s ) (1) 6.25 × 105 (2) 4.87 × 105 (3) 3.75 × 106 (4) 3.86 × 106

Q29.In a CE transistor amplifier, the audio signal voltage across the collector resistance of 2 kΩ is 2 V, if the base resistance is 1 kΩ and the current amplification of the transistor is 100 then the input signal voltage is (1) 10 mV (2) 1 mV (3) 0 .1 V (4) 1 V

Q29.An NPN transistor is used in common emitter configuration as an amplifier with 1 kΩ load resistance. Signal voltage of 10 mV is applied across the base-emitter. This produces a 3 mA change in the collector current and 15 μA change in the base current of the amplifier. The input resistance and voltage gain are: (1) 0.33 kΩ, 1.5 (2) 0.67 kΩ, 300 (3) 0.67 kΩ, 200 (4) 0.33 k Ω, 300

Q30.The resistance of the meter bridge AB in given figure is 4Ω. With a cell of emf ε = 0.5 V and rheostat resistance Rh = 2Ω the null point is obtained at some point J. When the cell is replaced by another one of emf ε = ε2 the same null point J is found for Rh = 6Ω. The emf ε2 is: (1) 0.4 V (2) 0.3 V (3) 0.6 V (4) 0.5 V

Q30.In a meter bridge experiment, the circuit diagram and the corresponding observation table are shown in figure. JEE Main 2019 (10 Apr Shift 1) JEE Main Previous Year Paper S. No. R(Ω) l(cm) 1. 1000 60 2. 100 13 3. 10 1.5 1 1.0 4. Which of the reading is inconsistent? (1) 1 (2) 3 (3) 2 (4) 4

Q30.The modulation frequency of an AM radio station is 250kHz, which is 10% of the carrier wave. If another AM station approaches you for license what broadcast frequency will you allot? (1) 2750 kHz (2) 2000 kHz (3) 2250 kHz (4) 2900kHz

Q30.The pitch and the number of divisions, on the circular scale, for a given screw gauge are 0. 5 mm and 100 respectively. When the screw gauge is fully tightened without any object, the zero of its circular scale lies 3 divisions below the mean line. The readings of the main scale and the circular scale, for a thin sheet, are 5 .5 mm and 48 respectively, the thickness of this sheet is: (1) 5.755 mm (2) 5.740 mm (3) 5.725 mm (4) 5.950 mm

Q30.The transfer characteristic curve of a transistor, having input and output resistance 100 Ω and 100 kΩ respectively, is shown in the figure. The voltage and power gain, are respectively: JEE Main 2019 (12 Apr Shift 1) JEE Main Previous Year Paper (1) 5 × 104, 2.5 × 106 (2) 2.5 × 104, 2.5 × 106 (3) 5 × 104, 5 × 106 (4) 5 × 104, 5 × 105 Q31.5 moles of AB2 weigh 125 × 10-3 kg and 10 moles of A2B2 weigh 300 × 10-3 kg . The molar mass of A ( MA ) in kg mol-1 are: (1) MA = 5 × 10-3 and MB = 10 × 10-3 (2) MA = 25 × 10-3 and MB = 50 × 10-3 (3) MA = 50 × 10-3 and MB = 25 × 10-3 (4) MA = 10 × 10-3 and MB = 5 × 10-3

Q30.A potentiometer wire AB having length L and resistance 12r is joined to a cell D of emf ε and internal resistance r. A cell C having EMF ε/2 and internal resistance 3r is connected. The length AJ, at which the galvanometer, as shown in the figure, shows no deflection is (1) 5 L (2) 11 L 12 24 (3) 11 L (4) 13 L 12 24

Q30.A tunning fork of frequency 480 Hz is used in an experiment for measuring speed of sound (v) in air by resonance tube method. Resonance is observed to occur at two successive lengths of the air column, l1 = 30 cm and l2 = 70 cm. Then, ν is equal to: (1) 384 m s−1 (2) 332 m s−1 (3) 338 m s−1 (4) 379 m s−1 Q31. 25 g of an unknown hydrocarbon upon burnig produces 88 g of CO2 and 9g of H2O. This unknown hydrocarbon contains: (1) 24 g of carbon and 1 g of hydrogen (2) 18 g of carbon annd 7 g of hydrogen (3) 22 g of carbon and 3 g of hydrogen (4) 20 g carbon and 5 g of hydrogen