datavorous/entrance-exam-dataset huggingface dataset:
Answer briefly :
(a) How do you perceive the colour of an object?
(b) Which part of our body helps us in maintaining the body balance?
(c) How does the eye regulate the amount of light that falls on the retina?

Options:

None

Solution:
(a) Cones are responsible for colour vision. They require brighter light than rods. There are three types of cones, maximally sensitive to longwavelength, medium-wavelength, and short-wavelength light (often referred to as red, green, and blue, respectively, though the sensitivity peaks are not actually at these colours). The colour seen is the combined effect of stimuli to, and responses from, these three types of cone cells. When these cones are stimulated equally, a sensation of white light is produced.
(b) The inner ear has three semi-circular canals forming cochlea. The inner ear also contains a complex system called vestibular apparatus, located above the cochlea. The vestibular apparatus is composed of three semi-circular canals and the otolith organ consisting of the saccule and utricle. The base of canals is swollen and is called ampulla, which contains a projecting ridge called crista ampullaris which has hair cells. The saccule and utricle contain a projecting ridge called macula. The crista and macula are the specific receptors of the vestibular apparatus responsible for maintenance of balance of the body and posture.
(c) The light rays in visible wavelength focussed on the retina through the cornea and lens generate potentials (impulses) in rods and cones. Light induces dissociation of the retinal from opsin resulting in changes in the structure of the opsin. This causes membrane permeability changes. As a result, potential differences are generated in the photoreceptor cells. These action potentials are transmitted by the optic nerves to the visual cortex area of the brain, where the neural impulses are analysed and the image formed on the retina is recognised based on earlier memory and experience.

Topic: Biology, Neural Control and Coordination
Answer the following:
(a) The casing of a rocket in flight burns up due to friction. At whose expense is the heat energy required for burning obtained? The rocket or the atmosphere?
(b) Comets move around the sun in highly elliptical orbits. The gravitational force on the comet due to the sun is not normal to the comet's velocity in general. Yet the work done by the gravitational force over every complete orbit of the comet is zero. Why?
(c) An artificial satellite orbiting the earth in very thin atmosphere loses its energy gradually due to dissipation against atmospheric resistance, however small. Why then does its speed increase progressively as it comes closer and closer to the earth?
(d) In Fig. given below (i) the man walks $2 \mathrm{~m}$ carrying a mass of $15 \mathrm{~kg}$ in his hands. In Fig. (ii), he walks the same distance pulling the rope behind him. The rope goes over a pulley, and a mass of $15 \mathrm{~kg}$ hangs at its other end. In which case is the work done greater?

Options:

None

Solution:
(a) The heat energy required for burning of the casing of a rocket in flight is obtained from the rocket itself. The energy is obtained at the expense of the mass of the rocket and its kinetic and potential energy.
(b) The gravitational force on the comet due to Sun is a conservative force. Since the work done by a conservative force over a closed path is always zero (irrespective of the nature of path). Hence the work done by the gravitational force over every complete orbit of the comet is zero of the comet. .
(c) As the satellite comes closer and closer to Earth, its potential energy decreases. Since according to the law of conservation of energy, the sum of kinetic and potential energy must remain constant, so the kinetic energy and hence velocity of the satellite increases. However, the total energy of the satellite continuously decreases some-what due to the loss of energy against friction i.e. atmospheric resistance.
(d) In the case shown in fig. (i), the man applies the force on the $15 \mathrm{~kg}$ mass in vertically upward direction but walks $2 \mathrm{~m}$ in the horizontal direction so the angle between $F$ and $S$ is $90^{\circ}$, hence work done $W=F . S$ is zero.
In fig. (ii), the force applied on the mass of $15 \mathrm{~kg}$ in the vertically upward direction (= weight of the body) and the mass is also lifted along the vertical so $\theta=0$
$\therefore \mathrm{W}=m g S=15 \times 9.8 \times 2=294 \mathrm{~J}$
Thus work done in second case is greater.

Topic: Physics, Work Power Energy
Answer the following questions:
(a) Explain qualitatively on the basis of domain picture the irreversibility in the magnetisation curve of a ferromagnet.
(b) The hysteresis loop of a soft iron piece has much smaller area than that of a carbon steel piece. If the material is to go through repeated cycles of magnetisation, which piece will dissipate greater heat energy?
(c) A system displaying a hysteresis loop such as a ferromagnet, is a device for storing memory?' Explain the meaning of this statement.
(d) What kind of ferromagnetic material is used for coating magnetic tapes in a cassette player, or for building 'memory stores' in modern computer?
(e) A certain region of space is to be shielded from magnetic fields. Suggest a method.

Options:

None

Solution:
(a) In a specimen of a ferromagnetic, the atomic dipoles are grouped together in domains. All the dipoles of a domain are aligned in the same direction and have net magnetic moment. In an unmagnetised substance these domains are randomly distributed so that the resultant magnetisation is zero. When the substance is placed in an external magnetic field, these domains align themselves in the direction of the field. Some energy is spent in the process of alignment when the external field is removed, these domains do nor come back into their random positions completely. The substance retains some magnetisation. The energy spent in the process of magnetisation is not fully recovered. The balance of energy is lost as heat. This is the basic cause for irreversibility of the magnetisation curve of a ferromagnetic substance.
(b) Carbon-Steel piece, because the heat produced in complete cycle of mangetisation is directly proportional to the area under the hysteresis loop.
(c) Magnetisation of a ferromagnet is not a single valued function of the magnetising field. Its value for a particular field depends both on the magnetising field and on the history of its magnetisation i.e. how many cycles of magnetisation it has gone through etc. So,
the value of magnetisation is a record or memory of its cycles if magnetisation. If information bits can be made to correspond to these cycles, the system displaying such a hysteresis loop can act as a device for storing information.
(d) Ferrites or ceramics which is specially treated barium iron oxides.
(e) By surrounding the region with soft iron rings, as magnetic field lines will be drawn into the rings and the enclosed space becomes free of magnetic field.

Topic: Physics, Magnetic Properties of Matter
Answer the following questions.
(a) In any ac circuit, is the applied instantaneous voltage equal to the algebraic sum of the instantaneous voltages across the series elements of the circuit? Is the same true for rms voltage?
(b) A capacitor is used in the primary circuit of an induction coil.
(c) An applied voltage signal consists of a superposition of a de voltage and an ac voltage of high frequency. The circuit consists of an inductor and a capacitor in series. Show that the dc signal will appear across $C$ and the ac signal across $L$.
(d) A choke coil in series with a lamp is connected to a dc line. The lamp is seen to shine brightly. Insertion of an iron core in the choke causes no change in the lamp's brightness. Predict the corresponding observations if the connection is to an ac line.
(e) Why is choke coil needed in the use of fluorescent tubes with ac mains? Why can we not use an ordinary resistor instead of the choke coil?

Options:

None

Solution:
(a) It is true that applied instantaneous voltage is equal to algebraic sum of instantaneous potential drop across each circuit element in series.
$$
\begin{aligned}
&E=V_R+V_L+V_C \\
&E_0 \sin \omega \mathrm{t}=\frac{E_0}{R} \sin \omega t \\
&\quad+\frac{E_0}{X_L} \sin \left(\omega t-\frac{\pi}{2}\right)+\frac{E_0}{X_C} \sin \left(\omega t+\frac{\pi}{2}\right)
\end{aligned}
$$
But the rms voltage applied is equal to vector sum of potential drop across each element, as voltage drops are in different phase.
(b) At the time of broken circuit of the induction coil the high voltage induced charges the capacitor. This avoid sparking in the circuit.
(c) Inductive reactance $X_{\mathrm{L}}=2 \pi f l$
For a.c. $X_C \propto f$ For d.c. $f=0, X_L=0$
Capacitive reactance $X_C=\frac{1}{2 \pi f C}$
For a.c. $X \propto \frac{1}{f}$
For d.c. $f=0 X_{\mathrm{C}}=\infty$
So, superimpose applied voltage will have all d.c potential drop across $X_{\mathrm{C}}$ and will have most of a.c potential drop across $X_{\mathrm{L}}$.
(d) Inductor offer no hinderance to d.c $X_L=0$, so insertion of iron core does not effect the d.c. current or brightness of lamp connected.
But it definitely effect a.c. current as inserted of iron core increases ' $L$ ' $L=\mu_{\mathrm{m}} n I$
thus increase $X_{\mathrm{L}}(2 \pi f$ L). a.c. current in the circuit reduce $I_{\mathrm{v}}=\frac{E_v}{X_L}$ and brightness of the bulb also reduce.
(e) A fluorescent tube is connected directly across a $220 \mathrm{~V}$ source, it would draw large current which may damage the filaments of the tube, so a choke coil which behaves as $L-R$ circuit reduces the current to appropriate value, and that also which a lesser power loss.
$$
I_v=\frac{E_v}{\sqrt{R^2+X_L^2}}, \quad \mathrm{P}=E_{\mathrm{v}} I_{\mathrm{v}} \cos \phi
$$
An ordinary resistor used to control the current would have maximum power wastage as heat
$$
I_v=\frac{E_v}{R}, P_{\max }=E_{\mathrm{v}} I_{\mathrm{v}}
$$

Topic: Physics, Alternating Current
Answer the following questions:
(a) Quarks inside protons and neutrons are thought to carry fractional charges $[(+2 / 3) e ;(-1 / 3) e]$. Why do they not show up in Millikan's oil-drop experiment?
(b) What is so special about the combination $\mathrm{e} / \mathrm{m}$ ? Why do we not simply talk of e and $m$ separately?
(c) Why should gases be insulators at ordinary pressures and start conducting at very low pressures?
(d) Every metal has a definite work function. Why do all photoelectrons not come out with the same energy if incident radiation is monochromatic? Why is there an energy distribution of photoelectrons?
(e) The energy and momentum of an electron are related to the frequency and wavelength of the associated matter wave by the relations $\mathbf{E}=\mathrm{h} \boldsymbol{v}, \mathrm{p}=\frac{\mathrm{h}}{\lambda}$
But while the value of $\lambda$ is physically significant, the value of $v$ (and therefore, the value of the phase speed $v \lambda$ ) has no physical significance. Why?

Options:

None

Solution:
(a) Quarks have fractional charges that are confined within a $\mathrm{p}^{+}$or $\mathrm{n}^0$. They are bound by nuclear forces which are strong and grow stronger if quarks are tried to pull apart. Thus quarks always remain together in form of fractional changes inside $\mathrm{p}^{+}$, $n^0$ only.
(b) The motion of $\mathrm{e}$ - inside electric and magnetic field is given by $\mathrm{eV}=\frac{1}{2} \mathrm{mv}^2$ and $\mathrm{eE}=\mathrm{ma}$ and $\mathrm{BeV}=$ $\frac{\mathrm{mv}^2}{\mathrm{r}}$. All these equations involve e and $\mathrm{m}$ together but not separately.
(c) Gases are generally insulators at atmospheric pressures because even if they are ionised, their positive and negative ions are close together and get ionised to form neutral atoms. At low pressures, the ionised gas particles are far apart and cannot recombine, hence they are free to conduct. Due to the presence of such free ions, gas can conduct.
(d) This is because work function gives the minimum energy required for the uppermost $\mathrm{e}^{-}$of the conduction band (least ionisation potential) to come out of the metal. Not all electrons ejected are from this level but from a different levels which requires different energy to come out. Hence, for same radiation incident, electrons may be knocked off from different levels and come out with different energy.
(e) The absolute value of energy E (only numerical part) has no significance except as an additive constant (P.S.- the sign of energy has physical meaning) put with momentum it is not so, Similarly for matter waves frequency has no direct physical meaning but wavelength is physically significant. The phase speed $v_\lambda=\mathrm{v}$ has no significance but group speed $=\frac{\mathrm{dE}}{\mathrm{dp}}=\frac{\mathrm{p}}{\mathrm{m}}$ has significance physically.

Topic: Physics, Dual Nature of Matter
Answer the following questions:
(a) The earth's magnetic field varies from point to point in space. Does it also change with time? If so, on what time scale does it change appreciably?
(b) The earth's core is known to contain iron. Yet geologists do not regard this as a source of the earth's magnetism. Why?
(c) The charged currents in the outer conducting regions of the earth's core are thought to be responsible for earth's magnetism. What might be the 'battery' (i.e., the source of energy) to sustain these currents?
(d) The earth may have even reversed the direction of its field several times during its history of 4 to 5 billion years. How can geologists know about the earth's field in such distant past?
(e) The earth's field departs from its dipole shape substantially at large distances (greater than about $30,000 \mathrm{~km}$ ). What agencies may be responsible for this distortion?
(f) Interstellar space has an extremely weak magnetic field of the order of $10^{-12}$ T. Can such a weak field be of any significant consequence? Explain.
[Note: Exercise $5.2$ is meant mainly to arouse your curiosity. Answers to some questions above are tentative or unknown. Brief answers wherever possible are given at the end. For details, you should consult a good text on geomagnetism.]

Options:

None

Solution:
(a) Yes, due to the motion of its plates and core the earth's magnetic field does shift. Noticeable changes occur over a large period of time (few hundred years ) and variations are there even in small durations of time (few years) which cannot be ignored.
(b) The core contains molten iron (magnetic domains are destroyed in molten form) which is not ferromagnetic hence it cannot contribute to magnetism of earth.
(c) No, one really knows.
(d) By study rock magnetism i.e., the solidification of rocks leads to trapping of materials in their magnetised states. Analysing these we can get clues to the history of geomagnetism.
(e) At large distances external factors such as solar winds, ionospheric particles etc. influences the earths magnetic field, hence it gets distorted.
(f) From cyclotron relation $r=\frac{m v}{e . B}$ we can say that small field can affect the path of moving charged particle whose radius is large eg. cosmic rays.

Topic: Physics, Magnetic Properties of Matter
Answer the following questions regarding earth's magnetism:
(a) A vector needs three quantities for its specification. Name the three independent quantities conventionally used to specify the earth's magnetic field.
(b) The angle of dip at a location in southern India is about $18^{\circ}$. Would you expect a greater or smaller dip angle in Britain?
(c) If you made a map of magnetic field lines at Melbourne in Australia, would the lines seem to go into the ground or come out of the ground?
(d) In which direction would a compass free to move in the vertical plane point to, if located right on the geomagnetic north or south pole?
(e) The earth's field, it is claimed, roughly approximates the field due to a dipole of magnetic moment $8 \times 10^{22} \mathrm{~J} \mathrm{~T}^{-1}$ located at its centre. Check the order of magnitude of this number in some way.
(f) Geologists claim that besides the main magnetic $\mathbf{N}-\mathrm{S}$ poles, there are several local poles on the earth's surface oriented in different directions. How is such a thing possible at all?

Options:

None

Solution:
(a) The three quantities are (1) magnetic declination (2) angle of dip and (3) horizontal component of earths magnetic field.
(b) Since Britian is closer to the magnetic north pole hence angle of dip would be greater.
(c) Since Australia is closer to magnetic south pole hence magnetic field lines would come out of the ground.
(d) At the geomagnetic poles the direction of magnetic field would be in the vertical direction hence a magnetic needle moving in a horizontal plane would point in any direction.
(e) Using formula for field at an equatorial point of a magnetic dipole
$$
\mathrm{B}=\frac{\mu_0 \mathrm{M}}{4 \pi \mathrm{r}^3} \text {, put } \mathrm{M} \approx 8 \times 10^{22} \mathrm{~J} / \mathrm{T}
$$
$$
\begin{aligned}
r &=6.4 \times 10^6 \mathrm{~m}, \frac{\mu_0}{4 \pi}=10^{-7} \\
& \Rightarrow \mathrm{B}=\frac{10^{-7} \times 8 \times 10^{22}}{\left(6.4 \times 10^6\right)^3} \\
& \approx \frac{8}{6.4 \times 6.4 \times 6.4} \times 10^{15-18} \\
& \approx 0.031 \times 10^{-3} \simeq 0.3 \times 10^{-4} \mathrm{~T} \simeq 0.3 \mathrm{G}
\end{aligned}
$$
This is close to value of field due to earth $(0.4 \mathrm{G})$ hence order of $m$ is correct.
(f) Local poles may happen due to deposites of magnetised mineral (iron etc.) Earths poles are the total sum of approximately all such magnetic fields inside the surface and in its core.

Topic: Physics, Magnetic Properties of Matter
Antibodies are synthesized by ________.

Options:
A Eosinophil
B Lymphocyte
C Monocyte
D Neutrophil

The correct answer is:
Lymphocyte

Solution:
A lymphocyte is a form of white blood cells with a single round nucleus, occurring especially in the lymphatic system. They produce antibody also known as an immunoglobulin (Ig), is a large, Y-shaped protein produced mainly by plasma cells that are used by the immune system to neutralize pathogens.

Topic: Biology, Human Health and Diseases, NEET
Antiseptic chloroxylenol is-

Options:
A 4- chloro-3, 5 - dimethyl phenol
B 3- chloro- 4, 5 - dimethyl phenol
C 4- chloro- 2, 5 - dimethyl phenol
D 5- chloro - 3, 4 - dimethyl phenol

The correct answer is:
4- chloro-3, 5 - dimethyl phenol

Solution:
Chloroxylenol, also known as para-chloro-meta-xylenol (PCMX), is an antiseptic and disinfectant which is used for skin disinfection and cleaning surgical instruments.

Topic: Chemistry, Chemistry in Everyday Life, JEE Main
Antiseptics and disinfectants either kill or prevent growth of microorganisms. Identify which of the following is not true.

Options:
A A $0.2 \%$ solution of phenol is an antiseptic while $1 \%$ solution acts as a disinfectant
B Chlorine and iodine are used as strong disinfectants
C Dilute solutions of boric acid and hydrogen, peroxide are strong antiseptics
D Disinfectants harm the living tissues

The correct answer is:
Dilute solutions of boric acid and hydrogen, peroxide are strong antiseptics

Solution:
Antiseptics and disinfectants both either kill or prevent the growth of microorganisms. The main point of difference between these two is that the former (antiseptics) are used for living beings whereas disinfectants are not safe for living tissues. These are actually used for inanimate objects like floors, tiles etc.
A substance like phenol in its lower concentration $(0.2 \%)$ behaves as antiseptic wheras in higher concentration (1\%) as disinfectant. Chlorine and iodine are strong disinfectants whereas dilute solutions of boric acid and hydrogen peroxide are mild antiseptics.

Topic: Chemistry, Chemistry in Everyday Life, NEET, NEET 2013 (All India)
Antiseptics and disinfectants either kill or prevent growth of microorganisms. Identify which of the following statement is
not true.

Options:
A dilute solutions of boric acid and hydrogen peroxide are strong antiseptics.
B Disinfectants harm the living tissues.
C A \( 0.2 \% \) solution of phenol is an antiseptic while \( 1 \% \) solution acts as a disinfectant
D Chlorine and iodine are used as strong disinfectants

The correct answer is:
dilute solutions of boric acid and hydrogen peroxide are strong antiseptics.

Solution:
Antiseptics and disinfectants both kill microorganism and also prevent them from further growing. The difference between them is that antiseptics are used for humans whereas disinfectants are not for humans and may cause damage to the human tissues. Also, 0.2% solution of phenol is an antiseptic while 1% solution acts as a disinfectant. Finally, dilute solutions of boric acid and hydrogen peroxide are very mild antiseptics.

Topic: Chemistry, Chemistry in Everyday Life, JEE Main
Any gas shows maximum deviation from ideal gas at

Options:
A $0^{\circ} \mathrm{C}$ and 1 atmospheric pressure
B $100^{\circ} \mathrm{C}$ and 2 atmospheric pressure
C $-100^{\circ} \mathrm{C}$ and 5 atmospheric pressure
D $500^{\circ} \mathrm{C}$ and 1 atmospheric pressure

The correct answer is:
$-100^{\circ} \mathrm{C}$ and 5 atmospheric pressure

Solution:
Real gases behave like ideal gases at high temperature and low pressure and maximum duration is observed when the condition is reversed means at low temperature and high pressure

Topic: Chemistry, States of Matter, JEE Main
Any precipitate is formed when

Options:
A Solution becomes saturated
B The value of ionic product is less that than the value of solubility product
C The value of ionic product is equal than the value of solubility product
D The value of ionic product is greater than the value of solubility product

The correct answer is:
The value of ionic product is equal than the value of solubility product

Solution:
The value of ionic product is equal than the value of solubility product

Topic: Chemistry, Ionic Equilibrium, JEE Main
Any series of operations so carried out that at the end, the system is back to its initial state is called

Options:
A Boyle's cycle
B Reversible process
C Adiabatic process
D Cyclic process

The correct answer is:
Cyclic process

Solution:
Cyclic process

Topic: Chemistry, Thermodynamics (C), JEE Main
Any vector in an arbitrary direction can always be replaced by two (or three)

Options:
A Parallel vectors which have the original vector as their resultant
B Mutually perpendicular vectors which have the original veckor as their resultant
C Arbitrary vectors which have the original vector as their resultant
D It is not possible to resolve a vector

The correct answer is:
Arbitrary vectors which have the original vector as their resultant

Solution:
If we slide a vector parallel to its position it will be the same as before. Any vector in an arbitrary direction can always be replaced by two (or three) arbitrary vectors which have the original vector as their resultant. Hence the option 3 is the correct option

Topic: Physics, Mathematics in Physics, JEE Main
Apart from plants and animals, microbes form a permanent biotic component in an ecosystem. While plants have been referred to as autotrophs and animals as heterotrophs. What are microbes referred to as? How do the microbes fulfill their energy requirements?

Options:

None

Solution:
Organisms are classified as autotrophs and heterotrophs, on the basis of nutrition. Autotrophs are further categorised into photoautotrophs and chemoautotrophs, while heterotrophs may be parasites, predators or a saprophytes etc.
Microbes are saprotrophs deriving nourishment or energy from dead organic matter or remains of plants and animals. Their mode of digestion is extracellular.

Topic: Biology, Ecosystem