NEET UG
- Radioactive material 'A' has decay constant '8λ' and material 'B' has decay constant 'λ'. Initially they have same number of nuclei. After what time, the ratio of number of nuclei of material 'B' to that 'A' will be 1/e ? Answer: 1. 1/7λ Key idea: N=N₀e^(-λ t) for each material, and take the ratio of the two. N_A=N₀e^(-8λ t) , N_B=N₀e^(-λ t) . Then N_A/N_B=e^(... 1
- The resistance of a wire is 'R' ohm. If it is melted and stretched to 'n' times its original length, its new resistance will be : Answer: 2. n²R Key idea: melting does not change the volume, so Al stays constant. If length becomes nl , area becomes A/n . Resistance R=ρl... 1
- The de-Broglie wavelength of a neutron in thermal equilibrium with heavy water at a temperature T (Kelvin) and mass m, is : Answer: 1. h/√(3mkT) Key idea: a thermal neutron has average kinetic energy 3/2kT , and λ=h/p=h/√(2mK) . λ=h/√(2m·3/2kT)=h/√(3mkT) . 1
- In an electromagnetic wave in free space the root mean square value of the electric field is E_rms = 6 V/m. The peak value of the magnetic field is : Answer: 1. 2.83×10⁻⁸ T Key idea: peak value =sqrt2× rms value, and B₀=E₀/c . E₀=6sqrt2=8.49 V/m. B₀=8.49/3×10⁸=2.83×10⁻⁸ T. 1
- The given electrical network is equivalent to : Answer: 2. NOR gate Key idea: trace the logic step by step. First gate is a NOR: output A+B . Second gate is a NOR with both inputs joined,... 1
- In a common emitter transistor amplifier the audio signal voltage across the collector is 3 V. The resistance of collector is 3 kΩ. If current gain is 100 and the base resistance is 2 kΩ, the voltage and power gain of the amplifier is : Answer: 2. 150 and 15000 Key idea: in a common emitter amplifier, voltage gain A_v=βR_C/R_B and power gain =β A_v . A_v=100×3\ kΩ/2\ kΩ=150... 1
- Two astronauts are floating in gravitational free space after having lost contact with their spaceship. The two will : Answer: 1. move towards each other. Key idea: the only force between the two astronauts is their mutual gravitational attraction. In free sp... 1
- An arrangement of three parallel straight wires placed perpendicular to plane of paper carrying same current 'I' along the same direction is shown in Fig. Magnitude of force per unit length on the middle wire 'B' is given by : Answer: 3. μ₀ i²/√(2)π d Key idea: parallel wires carrying current in the same direction attract each other, each pair giving a force per un... 1
- Young's double slit experiment is first performed in air and then in a medium other than air. It is found that 8^th bright fringe in the medium lies where 5^th dark fringe lies in air. The refractive index of the medium is nearly : Answer: 3. 1.78 Key idea: compare fringe positions using bright fringe y_n=nλ D/d and dark fringe y_n=(2n-1)λ D/2d . In air, 5th dark fringe... 1
- Two cars moving in opposite directions approach each other with speed of 22 m/s and 16.5 m/s respectively. The driver of the first car blows a horn having a frequency 400 Hz. The frequency heard by the driver of the second car is [velocity of sound 3… Answer: 3. 448 Hz Key idea: Doppler effect with source and observer approaching: f'=fv+v_o/v-v_s . f'=400×340+16.5/340-22=400×356.5/318≈448... 1
- Two rods A and B of different materials are welded together as shown in figure. Their thermal conductivities are K_1 and K_2. The thermal conductivity of the composite rod will be : Answer: 4. K₁+K₂/2 Key idea: the two rods are side by side, so heat flows through them in parallel, and the conductances add. Let each rod h... 1
- MALT constitutes about ______ percent of the lymphoid tissue in human body. Answer: 4. 50% Mucosa-associated lymphoid tissue (MALT) lines the respiratory, digestive and urogenital tracts. It forms about 50% of the ly... 1
- In case of poriferans, the spongocoel is lined with flagellated cells called : Answer: 2. choanocytes The spongocoel of sponges is lined by flagellated choanocytes (collar cells). Their beating drives water through the... 1
- Artificial selection to obtain cows yielding higher milk output represents : Answer: 1. directional as it pushes the mean of the character in one direction. Selecting cows for higher milk yield moves the mean of the t... 1
- Lungs are made up of air-filled sacs, the alveoli. They do not collapse even after forceful expiration, because of : Answer: 4. Residual Volume After a forceful expiration some air still stays in the lungs. This is the residual volume, about 1100 mL to 1200... 1
- Hypersecretion of Growth Hormone in adults does not cause further increase in height, because : Answer: 1. Epiphyseal plates close after adolescence. Height increases through growth at the epiphyseal plates of long bones. After adolesce... 1
- Good vision depends on adequate intake of carotene-rich food.Select the best option from the following statements.(a) Vitamin A derivatives are formed from carotene.(b) The photopigments are embedded in the membrane discs of the inner segment.(c) Ret… Answer: 1. (a), (c) and (d) Go statement by statement. (a) True: vitamin A derivatives form from carotene. (b) False: photopigments lie in t... 1
- Frog's heart when taken out of the body continues to beat for sometime.Select the best option from the following statements.(a) Frog is a poikilotherm.(b) Frog does not have any coronary circulation.(c) Heart is "myogenic" in nature.(d) Heart is auto… Answer: 3. (c) and (d) An isolated frog heart keeps beating because it is myogenic (the beat starts in the heart muscle itself) and autoexci... 1
- Which of the following in sewage treatment removes suspended solids ? Answer: 2. Primary treatment Primary treatment of sewage is physical: filtration and sedimentation remove floating and suspended solids. Sec... 1
- Which of the following options gives the correct sequence of events during mitosis ? Answer: 1. condensation → nuclear membrane disassembly → arrangement at equator → centromere division → segregation → telophase The correct... 1
- Which of the following components provides sticky character to the bacterial cell ? Answer: 3. Glycocalyx The glycocalyx is the outer layer of the bacterial cell envelope, made of polysaccharide (and sometimes protein). It i... 1
- Viroids differ from viruses in having : Answer: 3. RNA molecules without protein coat Viroids are smaller than viruses: they are infectious RNA molecules and have no protein coat.... 1
- Which of the following are found in extreme saline conditions ? Answer: 4. Archaebacteria Archaebacteria live in harsh habitats: extreme halophiles in very salty places, thermoacidophiles in hot springs,... 1
- Which among the following are the smallest living cells, known without a definite cell wall, pathogenic to plants as well as animals and can survive without oxygen ? Answer: 2. Mycoplasma The description fits Mycoplasma. Smallest living cells. No cell wall, so they are pleomorphic. Pathogenic to plants an... 1