datavorous/entrance-exam-dataset huggingface dataset:
An increase in the concentration of the toxicant at successive trophic levels is known as:

Options:
A Biodeterioration
B Biotransformation
C Biogeochemical cycling
D Biomagnification

The correct answer is:
Biomagnification

Solution:
Biomagnification is also called biological amplification or biological concentration. It is a phenomenon in which certain harmful chemicals get accumulated in the tissues of organisms in higher concentration through the food chain, Biocides including pesticides, fungicides, insecticides, rodenticides and herbicides shows biomagnification.

Topic: Biology, Environmental Issues, NEET, NEET 2015 (Phase 2)
An individual affected by phenylketonuria lacks an enzyme that converts the amino acid ________ into _______.

Options:
A tyrosine, phenylalanine
B phenylalanine, tyrosine
C homogentisicacid, phenylalanine
D homogentisic acid, tyrosine

The correct answer is:
phenylalanine, tyrosine

Solution:
Phenylketonuria is an inborn error of metabolism where the individual has reduced metabolism of the amino acid phenylalanine. Mutation in the gene causes inhibition of the production of enzyme phenylalanine hydroxylase that converts phenylalanine into tyrosine. Such mutation leads to mental retardation, with reduction in hair and skin pigmentation. It is a recessive autosomal disorder.

Topic: Biology, Principles of Inheritance and Variation, NEET
An individual having genotype AaBBccDD will produce ______ types of gametes.

Options:
A 2
B 4
C 8
D 16

The correct answer is:
2

Solution:
The given individual is hybrid for gene A, homozygous for gene B, homozygous for gene c and homozygous for gene D. Thus, this individual is a monohybrid. Monohybrids will produce only two types of gametes. The two types of gametes present in this example are ABcD and aBcD.

Topic: Biology, Principles of Inheritance and Variation, NEET
An individual heterozygous for two alleles AaBb produces two million sperms. How many of the sperms will have both the recessive alleles?

Options:
A 0.5 million
B 1 million
C 2 million
D 0.25 million

The correct answer is:
0.5 million

Solution:
A dihybrid AaBb will produce four types of gametes AB, Ab, aB, ab. All the gametes will be produced in equal proportion. Thus, 0.5 million gametes will have ab genotype.

Topic: Biology, Principles of Inheritance and Variation, NEET
An individual homozygous for gene a and b is crossed with wild type and F1 was back crossed with the double recessive. The appearance of the offsprings is as follows

++ → 39

ab → 31

a+ → 17

+b → 13

Find out the distance between genes a and b.

Options:
A 31
B 30
C 42.8
D 3

The correct answer is:
30

Solution:
(++) = 39; (ab) = 31; (a+) = 17;(b+) = 13.
Total number of progeny = 39 + 31 + 17 + 13 = 100.
No. of recombinants = (a+) + (b+) = 13 + 17 = 30.

Distance between a and b = No. of RecombinantsTotal no. of progeny x 100 =30100 x 100 = 30 cM

Topic: Biology, Principles of Inheritance and Variation, NEET
An individual homozygous for genes cd is crossed with wild type and F1 crossed back with the double recessive. The appearance of the offspring is as follows
+ + â 903
cd â 897
+d â 98
c+ â 102

The distance between the genes c and d is

Options:
A 20 map units
B 9.8 map units
C 10.2 map units
D 10 map units

The correct answer is:
10 map units

Solution:
% of recombination = Distance between two genes =Total no. of recombinant phenotypesTotal no. of progeny x 100 = 200 x 1002000 = 10 % or 10 cM

Topic: Biology, Principles of Inheritance and Variation, NEET
An individual with Down's syndrome has _______ copies of 21st chromosome.

Options:
A 1
B 4
C 3
D 2

The correct answer is:
3

Solution:
Down syndrome is usually caused by an error in cell division called "nondisjunction". Nondisjunction results in an embryo with three copies of chromosome 21 instead of the usual two. Prior to or at conception, a pair of 21st chromosomes in either the sperm or the egg fails to separate. As the embryo develops, the extra chromosome is replicated in every cell of the body. Thus Down syndrome is called trisomy of the 21st chromosome.

Topic: Biology, Principles of Inheritance and Variation, NEET
An inductor 20 mH, a capacitor 50 μF and a resistor 40 Ω are connected in series across a source of emf V=10 sin ⁡340 t. The power loss in AC . circuit is:

Options:
A 0.51ââW
B 0.67  W
C 0.76  W
D 0.89  W

The correct answer is:
0.51  W

Solution:
Given : R=40Ω , L= 20 mH , C=50 μF

Comparing the given equation for voltage with general equation V=V0 sin ωt

ω=340 rad s-1 and peak voltage V0=10 V

Inductive reactance XLωL=340×20×10-3=68×10-1=6.8 Ω
Capacitive reactance XC
1ωC=1340×50×10-6=10434×5=234×103
=0.0588×103=58.82 Ω
Z=XL-XC2+R2⇒Z=ωL-1ωC2+R2
Z=58.8-6.82+402 ⇒ Z=2704+1600≈65.6 Ω
Irms=VrmsZ=1065.6×2                   (Vrms=V02)
Power =ErmsIrms cos ϕ=Irms2R

∵cos ϕ=RZ, Vrms=IrmsZ

=100×4065.62×2=200065.62
=0.51 W

Topic: Physics, Alternating Current, NEET, NEET 2016 (Phase 1)
An inductor 20 mH, capacitor 100 μF and a resistor 50 Ω are connected in series across a source of emf, V= 10sin⁡(314t⁡). The power loss in the circuit is

Options:
A 2.74ââW
B 0.43ââW
C 0.79ââW
D 1.13  W

The correct answer is:
0.79  W

Solution:
V0=10 V, Ï=314 rad/s
P=VrmsIrmscosâ¡Ï
P= V rms V rms Z R Z
= ( V rms ) 2 R Z 2
XL=ÏL=314 20Ã10-3=6.280
XC=1ÏC=1314Ã100Ã10-6=31.84 Î©
R=50 Î©
Z= ( X C â X L ) 2 + R 2
= 31.84-6.282+502=56 Î©
âP= ( 10 2 ) 2 Ã 50 ( 56 ) 2 =0.79 W

Topic: Physics, Alternating Current, NEET, NEET 2018
An inductor coil and a capacitor and a resistance of 5 Î© are connected in series to an a.c. source of rms voltage 30 V. When the frequency of the source is varied, a maximum r.m.s. current of 5 A is observed. If this inductor is connected in parallel with a resistance 5 Î© to a battery of emf 25 V and internal resistance 2.0 Î©, the current drawn from the battery is

Options:
A 15017 A
B 2.5 A

C 12533 A
D 12599 A

The correct answer is:
15017 A

Solution:
Let resistance of inductor be μ
Imax=305+μ=5⇒μ=1 Ω
Now, I = 2 5 5 6 + 2
=15017 A

Topic: Physics, Alternating Current, NEET
An inductor coil stores 32 J of magnetic field energy and dissipates energy as heat at the rate of 320 W when a current of 4 A is passed through it. The time constant of the circuit when this coil is joined across an ideal battery will be

Options:
A 0.2 s
B 0.3Â s
C 0.4Â s
D 0.5Â s

The correct answer is:
0.2 s

Solution:
We know that U=12LI2
â32=12L42
âL=4 H
And power P=I2R
â320=42R
âR=20 Î©
We know that Ï=LR
âÏ=420
âÏ=0.2 s

Topic: Physics, Alternating Current, NEET
An inductor of inductance $2 \mathrm{mH}$ is connected to a $220 \mathrm{~V}, 50 \mathrm{~Hz}$ a.c. source. Let inductive reactance in the circuit is $X_1$. If a $220 \mathrm{~V}$ d.c. source replaces the a.c. source in the circuit, then the inductive reactance in the circuit is $\mathrm{X}_2 \cdot \mathrm{X}_1$ and $\mathrm{X}_2$ respectively are:

Options:
A $6.28 \Omega$, zero
B $6.28 \Omega$, infinity
C $0.628 \Omega$, zero
D $0.628 \Omega$, infinity

The correct answer is:
$0.628 \Omega$, zero

Solution:
For AC circuits,
$\begin{aligned} X_{\mathrm{L}} & =\omega \mathrm{L} \\ \mathrm{X}_{\mathrm{L}} & =2 \pi n \mathrm{~L} \\ \mathrm{X}_{\mathrm{L}} & =0.628 \Omega \\ \text {Hence, } & \mathrm{X}_1=0.628 \Omega\end{aligned} \quad(\because \omega=2 \pi n)$
For DC circuits, $\omega=0$
$\begin{aligned}
X_{\mathrm{L}} & =\omega \mathrm{L} \\
\mathrm{X}_{\mathrm{L}} & =0 \\
\mathrm{X}_2 & =0
\end{aligned}$
Hence $\quad X_2=0$

Topic: Physics, Alternating Current, NEET, NEET 2022 (Phase 2)
An inductor of inductance L, a capacitor of capacitance C and a resistor of resistance R are connected in series to an ac source of potential difference V volt as shown in figure.Potential difference across L,C and R is 40 V,10 V and 40 V, respectively. The amplitude of current flowing through L-C-R series circuit is 102 A. The impedance of the circuit is :

Options:
A 42Ω
B 5/2Ω
C 5Ω
D 4Ω

The correct answer is:
5Ω

Solution:
V=VR2+VC-VL2

=402+(10-40)2

=50 volt

irms=VrmsZ

⇒ Z=vrmsirms

⇒ Z=Vrms×210

⇒Z=2×50102

⇒Z=5 Ω

Topic: Physics, Alternating Current, NEET, NEET 2021
An infinite conducting sheet has surface charge density σ. The distance between two points is r. The potential difference VA-VB between these points is

Options:
A σr2ε0
B σrε0
C σε0r
D σ2ε0r

The correct answer is:
σr2ε0

Solution:
VA-VB=∫abE.dr=E b-a=σ r2ε0

Topic: Physics, Electrostatics, NEET
An infinite ladder network of resistances is constructed with 1 Î© and 2 Î© resistances. The 6 V battery has negligible internal resistance. The current that passes through the 2 Î© resistance nearest to the battery is

Options:
A 1Â A
B 1.5 A
C 2Â A
D 2.5Â A

The correct answer is:
1.5 A

Solution:
Let x be the equivalent resistance of the infinite ladder then,
the equivalent circuit is
also, the equivalent resistance is
x=1+2x2+x
x2-x-2=0
x=1+1+82=2 Î©
current through the battery is 3 A.
Current through 2 Î© resistor is
i=3x2+x=322+2=1.5 A

Topic: Physics, Current Electricity, NEET
An infinitely long cylinder of radius R is made of an unusual exotic material with refractive index –1 (Fig. 9.7). The cylinder is placed between two planes whose normals are along the y direction. The center of the cylinder O lies along the y-axis. A narrow laser beam is directed along the y direction from the lower plate. The laser source is at a horizontal distance x from the diameter in the y direction. Find the range of x such that light emitted from the lower plane does not reach the upper plane.

Options:
A Rπ/8 ≤ x ≤ R3π/8
B Rπ/4 ≤ x ≤ R3π/8
C R/8 ≤ x ≤ R3π/8
D R/4 ≤ x ≤ R3π/8

The correct answer is:
Rπ/8 ≤ x ≤ R3π/8

Solution:
Correct Option is : (A)
Rπ/8 ≤ x ≤ R3π/8

Topic: Chemistry, Ray Optics, NEET
An infinitely long line of linear charge density λ is shown in the figure. The potential difference VA-VB between the two points A and B is

Options:
A λ 2πε0 ln 2
B -λ 2πε0l n 2
C λ 4πε0l n 2
D -λ 4πε0l n 2

The correct answer is:
λ 2πε0 ln 2

Solution:
VA- VB =-∫BAE→.dr→
VA- VB =-∫2rr2λ4π ε0rdr
VA- VB =2λ4π ε0r ∫r2r1rdr
=2λ4π ε0 ln 2rr
=2λ4π ε0ln 2

Topic: Physics, Electrostatics, NEET
An infinitely long straight conductor carries a current of 5A as shown. An electron is moving with a speed of 105 m s-1 parallel to the conductor. The perpendicular distance between the electron and the conductor is 20 cm at an instant. Calculate the magnitude of the force experienced by the electron at that instant.

Options:
A 4×10-20 N
B 8π×10-20 N
C 4π×10-20 N
D 8×10-20 N

The correct answer is:
8×10-20 N

Solution:
Magnetic Field due to a current carrying wire at 20 cm in terms of current I is given by,

B=μ0I2πd

B=2×10-7×520×10-2

B=0.5×10-5 T

Now,

Force on charge particle =qvB

Fm=eVB

Fm=1.6×10-19×105×0.5×10-5

=8×10-20 N

Topic: Physics, Magnetic Effects of Current, NEET, NEET 2021
An infinitely long wire is kept along z-axis from z=- â to z= + â, having uniform linear charge density 109 nC m-1 The electric field Eâ at point 6 cm, 8 cm, 10 cm will be:

Options:
A (160 i^+120 j^+200 k^) N C-1
B (200 k^) N C-1
C (160 i^+120 j^) N C-1
D (120 i^+160 j^) N C-1

The correct answer is:
(120 i^+160 j^) N C-1

Solution:
E=2kλd=2×9×109×109×10-910 ×10-2=200 V m-1
As field is radial out, there is no component of it in Z direction.
E→=200 cos53 i^+200sin53 j^
=(120 i^+160 j^) N C-1

Topic: Physics, Electrostatics, NEET
An inorganic compound gives off O2 on heating. It also makes the colourless solution of potassium iodide to acquire purple tinge. The compound can be

Options:
A SO3
B K 2 C O 3
C H2O2
D H2O

The correct answer is:
H2O2

Solution:
This compound is hydrogen peroxide as on heating it gives O2 and it can also oxidise KI into I2 due to which purple tinge is formed.
H2O2→WarmH2O+12O2

Topic: Chemistry, s Block Elements, NEET
An inorganic compound (X) made of two most occurring elements in the earth's crust and used builiding construction when heated in an electric arc furnace with carbon , forms a poisonous gas (Y) which is most stable diatomic molecule. Compound (X) and gas (Y) will be

Options:
A SiO2, CO2
B Si, CO2
C SiO2, CO
D Si, CO

The correct answer is:
SiO2, CO

Solution:
Students are recommended to see the product given in option and think what is the possibility of starting material according to information provided in the question and chemical properties of starting material.
As the most occurring element in the earth crust is silicon as SiO2 and the chemical reaction of SiO2 with carbon produces CO which is poisonous gas as shown below
SiO 2 + 2 C → Si + 2 CO ↑ Poisonous gas and stable diaotmic molecule

Topic: Chemistry, p Block Elements (Group 13 & 14), NEET
An installation consisting of an electric motor driving a water pump left 75 L of water per second to a height of 4.7 m . If the motor consumes a power of 5 kW, then the efficiency of the installation is

Options:
A 39%
B 69%
C 93%
D 96%

The correct answer is:
69%

Solution:
Power consumed by the motor = 5 kW
=5×103 W
=5000 W
Power used in lifting the water
=mght
=75×9.8×4.7
=3454.5 kW
Efficiency =Power usedPower consumed×100%
=3454.55000×100=69%

Topic: Physics, Work Power Energy, NEET
An institution where valuable plant material likely to become irretrievably lost in the wild or cultivation is preserved in a viable condition is known as

Options:
A Genome
B Herbarium
C Gene library
D Gene bank

The correct answer is:
Gene bank

Solution:
An institution where valuable plant material likely to become irretrievably lost in the wild or cultivation is preserved in a viable condition is known as gene Bank.
Gene banks are a type of biorepository that preserves genetic materials. In plants, this could be by freezing cuts from the plant or stocking the seeds. In animals, this is by the freezing of sperm and eggs in zoological freezers until further need. With corals, fragments are taken, which are stored in water tanks under controlled conditions. Plant genetic material in a 'gene bank' is preserved at -196 °C in liquid nitrogen as mature seed (dry). In plants, it is possible to unfreeze the material and propagate it.

Topic: Biology, Biodiversity and its Conservation, NEET
An intense stream of water of cross section area A strikes a wall at an angle θ with the normal to the wall and rebounds elastically. If the density of water is ρ and its velocity is v , then the force exerted on the wall will be

Options:
A 2Av2Ï
B Av2Ï
C 2Av2ÏsinÎ¸
D 2Av2ρcosθ

The correct answer is:
2Av2ρcosθ

Solution:
Linear momentum of water striking per second to the wall
pi=mv=Avρv=Av2ρ ,
Linear momentum of reflected water per second
pr=Av2ρ
∴ Change in momentum of water per second
=ρicosθ+prcosθ
=2Av2ρcosθ
By the definition of force, force exerted on the wall
=2Av2ρcosθ

Topic: Physics, Laws of Motion, NEET
An interaction between two species wherein both species involved are benefited is called ___.

Options:
A Mutualism
B Commensalism
C Predation
D Parasitism

The correct answer is:
Mutualism

Solution:
An interaction between two species wherein both species involved are benefited is called Mutualism

Topic: Biology, Organisms and Populations, NEET
An interesting observation supporting evolution by natural selection comes from England. In a collection of moths made in the 1850s (before industrialization). Which of the following were true at that time?

P - Pollution was very less.
Q - Thick growth of almost white-colored lichen covered the moths.
R - Dark-coloured moths were picked out by predators.

Options:
A P only
B P, Q and R
C Q and R
D P and R

The correct answer is:
P and R

Solution:
Industrial melanism is an observation made in England that supports 'evolution by natural selection'.
A. The collection is done in the 1850s (before industrialization sets in): On trees, white-winged moths were more in number than dark-winged (or melanized) moths. Before industrialization, white-colored lichen grows and almost covered the trees because of which white-winged moth survived due to white background the but the dark-colored moth was more spotted and picked up by the predators.
B. The collection is done in the 1920s (After Industrialization): On trees, Dark -winged moths were more than white-winged moths. Lichens do not grow in polluted areas, so the dark moths were able to camouflage (hide in the background) themselves against the tree trunks became dark due to industrial smoke and soots. Thus they survived in more numbers. White-winged moths were more spotted and picked up by the predators in comparison to the dark-winged.

Topic: Biology, Evolution, NEET
An internal process that regulates the sleep-wake cycle and repeats roughly every 24 hours is regulated by

Options:
A Melatonin
B ADH
C Thyroxine
D Oxytocin

The correct answer is:
Melatonin

Solution:
Melatonin is created by the pineal gland in the brain. In a healthy, normally functioning individual, melatonin is released in a rhythmic cycle, with more melatonin produced at night when the light entering the eyes starts to diminish. The bloodstream carries it to the different areas of the body, where receptors pick up the melatonin to signal the need for sleep.

Topic: Biology, Chemical Coordination and Integration, NEET
An intrinsic semiconductor is converted into n-type extrinsic semiconductor by doping it with:-

Options:
A Phosphorous
B Aluminium
C Silver
D Germanium

The correct answer is:
Phosphorous

Solution:
Pentavalent impurities are the atoms with five valence electrons used for the doping of semiconductors. i.e. Arsenic (As), Phosphorous (Pi), Antimony (Sb), etc. Arsenic is an example of pentavalent impurity. They have 5 valence electrons. For n-type semi-conductor intrinsic semiconductor is doped by pentavalent impurity.

Topic: Physics, Semiconductors, NEET, NEET 2020 (Phase 2)
An inverted bell, lying at the bottom of lake 47.6 m deep, has 50 cm 3 of air trapped in it. The bell is brought to the surface of lake. The volume of the trapped air will become (atmospheric pressure = 70 cm of Hg and density of Hg=13.6g/ cm 3 )

Options:
A 350 cm 3
B 300 cm 3
C 250 cm 3
D 22 cm 3

The correct answer is:
300 cm 3

Solution:
According to Boyle's law, pressure and volume are inversely proportional to each other i.e. p â 1 v

â P 1 V 1 = P 2 V 2
â ( P 0 + h Ï w g ) V 1 = P 0 V 2
â V 2 = ( 1 + h Ï w g P 0 ) V 1
V 2 = 1+ 47.6*1*1000*10 70* 10 â2 *13.6*1000*10 V 1
[Asâ P 2 = P 0 =70ââcmââofâHg=70* 10 â2 *13.6*1000*10]
â V 2 = 1 + 5 5 0 cm 3 = 3 0 0 cm 3

Topic: Physics, Thermodynamics, NEET
An inverted bell, lying at the bottom of lake 47.6 m deep, has 50 cm3 of air trapped in it. The bell is brought to the surface of the lake, then the volume of the trapped air will become [atmospheric pressure = 70 cm of Hg and density of Hg=13.6 g cm-3]

Options:
A 600 cm3
B 300 cm3
C 250 cm3
D 200 cm3

The correct answer is:
300 cm3

Solution:
According to Boyle's law, pressure and volume are inversely proportional to each other i.e. p ∝ 1 v

⇒P1V1=P2V2
⇒(P0+hρwg)V1=P0V2
⇒V2=(1+hρwgP0)V1
V2=(1+47.6*1*1000*1070*10−2*13.6*1000*10)[As P2=P0=70  cm  of Hg=70*10−2*13.6*1000*10]
⇒V2=1+550 cm3=300 cm3

Topic: Physics, Thermodynamics, NEET
An inverted pyramid of biomass can be found in which ecosystem?

Options:
A Forest
B Marine
C Grassland
D Tundra

The correct answer is:
Marine

Solution:
In terrestrial ecosystem pyramid of biomass is generally upright. The pyramid of biomass in sea or lake is generally inverted because the biomass of fishes for exceeds that of phytoplankton.

Topic: Biology, Ecosystem, NEET
An inverted pyramid of _____________ may be observed in ____________ communities.

Options:
A Energy, grassland
B Energy, forest
C Biomass, marine
D Biomass, forest

The correct answer is:
Biomass, marine

Solution:
The pyramid of energy is always upright for all communities as producers always have higher energy. For aquatic communities number of phytoplanktons are more in number but their biomass is less as compared to consumers, thus pyramid of biomass is inverted for aquatic communities.

Topic: Biology, Ecosystem, NEET
An inverted pyramid of number and an inverted pyramid of biomass are respectively seen in:

Options:
A Grassland Tree ecosystem
B Sea and Tree ecosystem
C Tree and Sea ecosystem
D Sea and Grassland ecosystem

The correct answer is:
Tree and Sea ecosystem

Solution:
Ecological pyramids are of 3 types (a) Pyramid of Energy: Always upright, without any exception, because at successive trophic levels only 10% energy is transferred. (b) Pyramid of number: Mostly upright, except - tree ecosystem, in which on the single large tree several birds survive and on these birds several parasites are present. (c) Pyramid of Biomass: Mostly upright, except - Sea/aquatic ecosystem, in which producers are planktons which have very less weight although dependent smaller and larger fishes have comparatively more weight.

Topic: Biology, Ecosystem, NEET
An ion with mass number 37 possesses one unit of negative charge. If the ion conatins 11.1% more neutrons than the electrons, what is the symbol of the ion?

Options:
A (37Cl17)-1
B (39Cl17)-1
C (37Cl17)-2
D (37Cl23)-1

The correct answer is:
(37Cl17)-1

Solution:
Correct Option is : (A)
(37Cl17)-1

Topic: Chemistry, Structure of Atom, NEET
An ion with mass number 56 contains 3 units of positive charge and 30.4% more neutrons than electrons. what is the symbol of the ion?

Options:
A (56Fe31)3+
B (56Fe26)2+
C (59Fe26)3+
D (56Fe26)3+

The correct answer is:
(56Fe26)3+

Solution:
Correct Option is : (D)
(56Fe26)3+

Topic: Chemistry, Structure of Atom, NEET
An ionic compound has a unit cell consisting of A ions at the corners of a cube, B ions on the centres of the faces of the cube but one axis of its faces are missing. The empirical formula for this compound would be -

Options:
A AB2
B A3B
C AB
D A2B

The correct answer is:
AB2

Solution:
Numbers of ions of A=8×18=1 ;
Numbers of ions of B=4×12=2 ;
∴ Formula is AB2

Topic: Chemistry, Solid State, NEET
An ionic hydride of an alkali metal has significant covalent character and is almost unreactive towards oxygen and chlorine. This is used in the synthesis of other useful hydrides. Write the formula of this hydride. Write its reaction with Al2Cl6.

Options:
A NaH; NaH + Al2Cl6→ 2AlCl3+ 2NaCl
B KH; KH + Al2Cl6→ 2AlCl3+ KCl
C LiH; LiH + Al2Cl6→ 2AlCl3+ LiCl
D RbH; RbH + Al2Cl6→ 2AlCl3+ RbCl

The correct answer is:
NaH; NaH + Al2Cl6→ 2AlCl3+ 2NaCl

Solution:
Correct Option is : (A)
NaH; NaH + Al2Cl6→ 2AlCl3+ 2NaCl

Topic: Chemistry, Hydrogen, NEET
An ionisation chamber, with parallel conducting plates as anode and cathodes, has 5Ã107 cm-3 electrons and the same number of singly charged positive ions per cm3 .The electrons are moving toward the anode with velocity 0.4 m s-1. If current density J=4Ã10-6 A m-2 then the velocity of positive ions moving towards cathode is

Options:
A 0.1 m s-1
B 0.4 m s-1
C Zero
D 1.6 m s-1

The correct answer is:
0.1 m s-1

Solution:
Here, No. of electrons
ne=5Ã107cm-3=5Ã107Ã106 m-3
No. of positive ions, np=5Ã107Ã106 m -3
=5Ã1013 m-3
v e =0.4 m s-1;J=4Ã10-6 A m-2;vp=? Use the relation
J=nee ve+np e vp and solve it for vp
4Ã10-6=5Ã1013Ã1.6Ã10-19Ã0.4+(5Ã1013Ã1.6Ã10-19Ãvp)
vp=4Ã10-6-3.2Ã10-68.0Ã10-6=0.8Ã10-68Ã10-6=0.1 m s-1

Topic: Physics, Current Electricity, NEET
An ionized gas contains both positive and negative ions. If it is subjected simultaneously to an electric field along the +x direction and a magnetic field along the +z direction, then

Options:
A Positive ions deflect towards +y direction and negative ions towards -y direction
B All ions deflect towards +y direction
C All ions deflect towards -y direction
D Positive ions deflect towards -y direction and negative ions towards +y direction

The correct answer is:
All ions deflect towards -y direction

Solution:
As electric field will accelerate +ve charge along +ve x- axis and -ve charge along -ve x axis from F → = q v → × B → direction of q(V→×​B→) will be same for both of them i.e. -ve y direction so both will deflect towards -ve y direction.

Topic: Physics, Magnetic Effects of Current, NEET