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Q.1 A current of 'i' ampere is flowing through each of the bent wires as shown the magnitude and direction
of magnetic field at O is
(A)
R
2
R
1
4
i0(B)
R
3
R
1
4
i0
(C)
R2
3
R
1
8
i0(D)
R
3
R
1
8
i0
Q.2 A charge particle A of charge q = 2 C has velocity v = 100 m/s. When it passes through point A and has
velocity in the direction shown. The strength of magnetic field at point B due to this moving charge is
(r = 2 m).
(A) 2.5 T (B) 5.0 T
(C) 2.0 T (D) None
Q.3 Three rings, each having equal radius R, are placed mutually perpendicular to each other and each
having its centre at the origin of co-ordinate system. If current I is flowing thriugh each ring then the
magnitude of the magnetic field at the common centre is
(A) R2
I3 0
(B) zero
(C) R2
I12 0 (D)
R2
I23 0
Q.4 Two concentric coils X and Y of radii 16 cm and 10 cm lie in the same vertical plane containing N-S
direction. X has 20 turns and carries 16 A. Y has 25 turns & carries 18A. X has current in anticlockwise
direction and Y has current in clockwise direction for an observer, looking at the coils facing the west.
The magnitude of net magnetic field at their common centre is
(A) 5 × 10–4 T towards west (B) 13 × 10–4 T towards east
(C) 13 × 10–4 T towards west (D) 5 × 10–4 T towards east
Q.5 A current I flows around a closed path in the horizontal plane of the circle as shown in the figure. The
path consists of eight arcs with alternating radii r and 2r. Each segment of arc subtends equal angle at the
common centre P. The magnetic field produced by current path at point P is
(A) r
I
8
3 0 ; perpendicular to the plane of the paper and directed inward.
(B) r
I
8
3 0 ; perpendicular to the plane of the paper and directed outward.
TOPIC : MAGNETIC EFFECT OF CURRENT, MAGNETISM & PHOTOELECTRIC EFFECT
PHYSICSQuestion Bank-5
Target IIT JEE-2020Rank Boosting Course (RBC)
2
(C) r
I
8
1 0 ; perpendicular to the plane of the paper and directed inward.
(D) r
I
8
1 0 ; perpendicular to the plane of the paper and directed outward.
Q.6 Infinite number of straight wires each carrying current I are equally placed as shown in the figure.
Adjacent wires have current in opposite direction. Net magnetic field at point P is
(A) ka3
2n
4
I0 l
(B) ka3
4n
4
I0 l
(C) )k(a3
4n
4
I0
l
(D) Zero
Q.7 Two mutually perpendicular conductors carrying currents I1 and I2 lie in one plane. Locus of the point at
which the magnetic induction is zero, is a
(A) circle with centre as the point of intersection of the conductor.
(B) parabola with vertex as the point of intersection of the conductors
(C) straight line passing through the point of intersection of the conductors.
(D) rectangular hyperbola
Q.8 Find the magnetic field at P due to the arrangement shown
(A)
2
11
d2
i0 (B)
d2
i2 0
(C)
d2
i0 (D)
2
11
d2
i0
Q.9 Equal current i is flowing in three infinitely long wires along positive x, y and z directions. The magnetic
field at a point (0, 0, –a) would be:
(A) )ij(a2
i0
(B) )ji(
a2
i0
(C) )ji(
a2
i0
(D) )kji(
a2
i0
Q.10 Two very long straight parallel wires, parallel to y-axis, carry currents 4I and I, along +y direction and
–y direction, respectively. The wires are passes through the x-axis at the points (d, 0, 0) and (– d, 0, 0)
respectively. The graph of magnetic field z-component as one moves along the x-axis from x = – d to
x = +d, is best given by
(A) (B) (C) (D)
3
Q.11 A long thin walled pipe of radius R carries a current I along its length. The current density is uniform over
the circumference of the pipe. The magnetic field at the center of the pipe due to quarter portion of the
pipe shown, is
(A) R4
2I2
0
(B)
R
I20
(C) R
2I22
0
(D) None
Q.12 Two long conductors are arranged as shown above to form overlapping cylinders, each of raidus r,
whose centers are separated by a distance d. Current of density J flows into the plane of the page along
the shaded part of one conductor and an equal current flows out of the plane of the page along the
shaded portion of the other, as shown. What are the magnitude and direction of the magnetic field at
point A?
(A) (0/2)dJ, in the +y-direction
(B) (0/2)d2/r, in the +y-direction
(C) (0/2)4d2J/r, in the –y-direction
(D) (0/2)Jr2/d, in the –y-direction
(E) There is no magnetic field at A.
Q.13 An electron is moving along positive x-axis. A uniform electric field exists towards negative y-axis. What
should be the direction of magnetic field of suitable magnitude so that net force of electron is zero
(A) positive z- axis (B) negative z-axis (C) positive y-axis (D) negative y-axis
Q.14 A particle of charge q and mass m starts moving from the origin under the action of an electric field
iEE 0
and iBB 0
with velocity j0vv
. The speed of the particle will become 2v0 after a time
(A) t = qE
m2 0v(B) t =
0m
Bq2
v (C) t = 0m
Bq3
v(D) t =
qE
m3 0v
Q.15 An electron is projected with velocity v0 in a uniform electric field E perpendicular to the field. Again it is
projetced with velocity v0 perpendicular to a uniform magnetic field B. If r1 is initial radius of curvature
just after entering in the electric field and r2 is initial radius of curvature just after entering in magnetic field
then the ratio 21 rr is equal to
(A) E
Bv20 (B)
E
B(C)
B
Ev0(D)
E
Bv0
Q.16 A uniform magnetic field jBB 0
exists in a space. A particle of mass m and charge q is projected
towards negative x-axis with speed v from the a point (d, 0, 0). The maximum value v for which the
particle does not hit y-z plane is
(A) dm
qB2 0(B)
m
qdB0(C)
dm2
qB0(D)
m2
qdB0
4
Q.17 Two protons move parallel to each other, keeping distance r between them, both moving with same
velocity V
. Then the ratio of the electric and magnetic force of interaction between them is
(A) 22 Vc (B) 22 Vc2 (C) 22 V2c (D) None
Q.18 Three ions H+, He+ and O+2 having same kinetic energy pass through a region in which there is a uniform
magnetic field perpendicular to their velocity, then :
(A) H+ will be least deflected. (B) He+ and O+2 will be deflected equally.
(C) O+2 will be deflected most. (D) all will be deflected equally.
Q.19 An electron having kinetic energy T is moving in a circular orbit of radius R perpendicular to a uniform
magnetic induction B
. If kinetic energy is doubled and magnetic induction tripled, the radius will become
(A) 2
R3(B)
2
3 R (C)
9
2 R (D)
3
4 R
Q.20 An electron (mass = 9.1 × 1031 ; charge = 1.6 × 1019 C) experiences no deflection if subjected to
an electric field of 3.2 × 105 V/m and a magnetic field of 2.0 × 103 Wb/m2 . Both the fields are normal
to the path of electron and to each other . If the electric field is removed, then the electron will revolve in
an orbit of radius :
(A) 45 m (B) 4.5 m (C) 0.45 m (D) 0.045 m
Q.21 A electron experiences a force j0.3i0.4 × 10–13 N in a uniform magnetic field when its velocity is
710k5.2 ms–1. When the velocity is redirected and becomes 710j0.2i5.1 ms–1, the magnetic
force of the electron is zero. The magnetic field vector
B is :
(A) – j1.0i075.0 (B) j075.0i1.0 (C) kj1.0i075.0 (D) j1.0i075.0
Q.22 Electrons moving with different speeds enter a uniform magnetic field in a direction perpendicular to the
field. They will move along circular paths.
(A) of same radius
(B) with larger radii for the faster electrons
(C) with smaller radii for the faster electrons
(D) either (B) or (C) depending on the magnitude of the magnetic field
Q.23 In the previous question, time periods of rotation will be :
(A) same for all electrons
(B) greater for the faster electrons
(C) smaller for the faster electrons
(D) either (B) or (C) depending on the magnitude of the magnetic field
Q.24 OABC is a current carrying square loop an electron is projected from the centre of loop along its
diagonal AC as shown. Unit vector in the direction of initial acceleration will be
(A) k (B)
2
ji
(C) – k (D) 2
ji
5
Q.25 A particle having charge of 1 C, mass 1 kg and speed 1 m/s enters a uniform magnetic field, having
magnetic induction of 1 T, at an angle = 30° between velocity vector and magnetic induction. The pitch
of its helical path is (in meters)
(A) 2
3(B) 3 (C)
2
(D)
Q.26 A charged particle is released from rest in a region of uniform electric and magnetic fields, which are
parallel to each other. The locus of the particle will be
(A) helix of constant pitch (B) straight line
(C) helix of varying pitch (D) cycloid
Q.27 A particle of specific charge (charge/mass) starts moving from the origin under the action of an electric
field iEE 0
and magnetic field kBB 0
. Its velocity at (x0, y0, 0) is )j3i4( . The value of x0 is:
(A) 0
0
B
E
2
13 (B)
0
0
E
B16(C)
0E2
25
(D) 0B2
5
Q.28 A particle of specific charge (q/m) is projected from the origin of coordinates with initial velocity
[ui – vj]. Uniform electric magnetic fields exist in the region along the +y direction, of magnitude E and B.
The particle will definitely return to the origin once if
(A) ]E2vB[ is an integer (B) (u2 + v2)1/2 ]EB[ is an integer
(C) ]EvB[ in an integer (D) ]EuB[ is an integer
Q.29 An electron moving with a velocity i2V1
m/s at a point in a magnetic field experiences a force
Nj2F1
. If the electron is moving with a velocity j2V2
m/s at the same point, it experiences a
force Ni2F2
. The force the electron would experience if it were moving with a velocity
k2V3
m/s at the same point is
(A) zero (B) Nk2
(C) Nk2 (D) information is insufficient
Q.30 Two particles of charges +Q and –Q are projected from the same point with a velocity v in a region of
uniform magnetic field B such that the velocity vector makes an angle with the magnetic field. Their
masses are M and 2M, respectively. Then, they will meet again for the first time at a point whose
distance from the point of projection is
(A) QBcosMv2 (B) QBcosMv8 (C) QBcosMv (D) QBcosMv4
Q.31 A block of mass m & charge q is released on a long smooth inclined plane magnetic field B is constant,
uniform, horizontal and parallel to surface as shown. Find the time from start when block loses contact
with the surface.
(A) qB
cosm (B)
qB
eccosm
(C) qB
cotm (D) none
6
Q.32 A metal ring of radius r = 0.5 m with its plane normal to a uniform magnetic field B of induction 0.2 Tcarries a current I = 100 A. The tension in newtons developed in the ring is:
(A) 100 (B) 50 (C) 25 (D) 10
Q.33 In given figure, X and Y are two long straight parallel conductors each carrying a current of 2 A. The
force on each conductor is F newtons. When the current in each is changed to 1 A and reversed in
direction, the force on each is now
(A) F/4 and unchanged in direction (B) F/2 and reversed in direction
(C) F/2 and unchanged in direction (D) F/4 and reversed in direction
Q.34 A conducting ring of mass 2 kg and radius 0.5 m is placed on a smooth horizontal plane. The ring carries
a current i = 4A. A horizontal magnetic field B = 10T is switched on at time t = 0 as shown in figure. The
initial angular acceleration of
the ring will be
(A ) 40 rad/s2 (B) 20 rad/s2
(C) 5 rad/s2 (D) 15 rad/s2
Q.35 A straight rod of mass m and length L is suspended from the identical spring as shown in the figure. The
spring stretched by a distance of x0 due to the weight of the wire. The circuit has total resistance R.
When the magnetic field perpendicular to the plane of the paper is switched on, springs are observed to
extend further by the same distance. The magnetic field strength is
(A) L
mgR
; directed outward from the plane of the paper
(B) 0x2
mgR
; directed outward from the plane of the paper
(C) L
mgR
; directed into the plane of the paper
(D) 0x
mgR
; directed into the plane of the paper
Q.36 A conducting wire bent in the form of a parabola y2 = 2x carries a current i = 2 A as shown in figure. This
wire is placed in a uniform magnetic field k4B
Tesla. The magnetic force on the wire is (in newton)
(A) i16 (B) i32 (C) i32 (D) i16
Q.37 A rectangular coil PQ has 2n turns, an area 2a and carries a current 2I, (refer
figure). The plane of the coil is at 60° to a horizontal uniform magnetic field of
flux density B. The torque on the coil due to magnetic force is
(A) BnaI sin60° (B) 8BnaI cos60° (C) 4naI Bsin60° (D) none
7
Q.38 A straight current carrying conductor is placed in such a way that the current in the conductor flows in the
direction out of the plane of the paper. The conductor is placed between two poles of two magnets, as
shown. The conductor will experience a force in the direction towards
(A) P (B) Q (C) R (D) S
Q.39 Figure shows a square current carrying loop ABCD of side 10 cm and
current i = 10A. The magnetic moment M
of the loop is
(A) (0.05) 2mAk3i (B) (0.05) 2mAkj
(C) (0.05) 2mAki3 (D) 2mAki
Q.40 In a region of space, a uniform magnetic field B exists in the y-direction. A proton is fired from the origin,
with its initial velocity v making a small angle with the y-direction in the yz plane. In the subsequent
motion of the proton,
(A) its x-coordinate can never be positive
(B) its x- and z-coordinates cannot both be zero at the same time
(C) its z-coordinate can never be negative
(D) its y-coordinate will be proportional to the square of its time of flight
Q.41 Let nr and nb be respectively the number of photons emitted by a red bulb and a blue bulb of equal
power in a given time.
(A) nr = nb (B) nr < nb
(C) nr > nb (D) data insufficient
Q.42 10–3 W of 5000 Å light is directed on a photoelectric cell. If the current in the cell is 0.16 A, the
percentage of incident photons which produce photoelectrons, is
(A) 0.4% (B) .04% (C) 20% (D) 10%
Q.43 In a photo-emissive cell, with exciting wavelength , the maximum kinetic energy of electron is K. If the
exciting wavelength is changed to 4
3 the kinetic energy of the fastest emitted electron will be:
(A) 3K/4 (B) 4K/3 (C) less than 4K/3 (D) greater than 4K/3
Q.44 If the frequency of light in a photoelectric experiment is doubled, the stopping potential will
(A) be doubled (B) halved
(C) become more than doubled (D) become less than double
Q.45 The maximum kinetic energy of photoelectrons emitted from a surface when photons of energy 6 eV
fall on it is 4 eV. The stopping potential in Volts is :
(A) 2 (B) 4 (C) 6 (D) 10
Q.46 The stopping potential for the photo electrons emitted from a metal surface of work function 1.7 eV is
10.4 V. Identify the energy levels corresponding to the transitions in hydrogen atom which will result in
emission of wavelength equal to that of incident radiation for the above photoelectric effect
(A) n = 3 to 1 (B) n = 3 to 2
8
(C) n = 2 to 1 (D) n = 4 to 1
Q.47 When a photon of light collides with a metal surface, number of electrons, (if any) coming out is
(A) only one (B) only two
(C) infinite (D) depends upon factors
Q.48 The frequency and the intensity of a beam of light falling on the surface of photoelectric material are
increased by a factor of two. Treating efficiency of photoelectron generation as constant, this will :
(A) increase the maximum energy of the photoelectrons, as well as photoelectric current by a factor of
two.
(B) increase the maximum kinetic energy of the photo electrons and would increase the photoelectric
current by a factor of two.
(C) increase the maximum kinetic energy of the photoelectrons by a factor of greater than two and will
have no effect on the magnitude of photoelectric current produced.
(D) not produce any effect on the kinetic energy of the emitted electrons but will increase the photoelectric
current by a factor of two.
Q.49 A point source of light is used in a photoelectric effect. If the source is removed farther from the emitting
metal, the stopping potential :
(A) will increase (B) will decrease
(C) will remain constant (D) will either increase or decrease.
Q.50 A point source causes photoelectric effect from a small metal plate. Which of the following curves may
represent the saturation photocurrent as a function of the distance between the source and the metal ?
(A)
i
r
(B)
i
r
(C)
i
r
(D)
i
r
Q.51 In a photoelectric experiment, the potential difference V that must be maintained between the illuminated
surface and the collector so as just to prevent any electron from reaching the collector is determined for
different frequencies f of the incident illumination. The graph obtained is shown. The maximum kinetic
energy of the electrons emitted at frequency f1 is
(A) hf1 (B) )ff(
V
01
1
(C) h (f1 – f0) (D) eV1(f1 – f0)
Q.52 Radiation of two photon energies twice and five times the work function of metal are incident sucessively
on the metal surface. The ratio of the maximum velocity of photoelectrons emitted is the two cases will
be
(A) 1 :2 (B) 2 : 1 (C) 1 : 4 (D) 4 : 1
Q.53 Cut off potentials for a metal in photoelectric effect for light of wavelength 1, 2 and 3 is found to be
V1, V2 and V3 volts if V1, V2 and V3 are in Arithmetic Progression and 1, 2 and 3 will be:
(A) Arithmetic Progression (B) Geometric Progression
9
(C) Harmonic Progression (D) None
Q.54 Photons with energy 5 eV are incident on a cathode C , on a photoelectric cell. The maximum energy of
the emitted photoelectrons is 2 eV. When photons of energy 6 eV are incident on C, no photoelectrons
will reach the anode A if the stopping potential of A relative to C is
(A) 3 V (B) – 3V (C) – 1V (D) 4 V
Q.55 In a photoelectric experiment, the collector plate is at 2.0V with respect to the emitter plate made of
copper = 4.5eV). The emitter is illuminated by a source of monochromatic light of wavelength 200nm.
(A) the minimum kinetic energy of the photoelectrons reaching the collector is 0.
(B) the maximum kinetic energy of the photoelectrons reaching the collector is 3.7eV.
(C) if the polarity of the battery is reversed then answer to part A will be 0.
(D) if the polarity of the battery is reversed then answer to part B will be 1.7eV.
Q.56 By increasing the intensity of incident light keeping frequency (v > v0) fixed on the surface of metal
(A) kinetic energy of the photoelectrons increases
(B) number of emitted electrons increases
(C) kinetic energy and number of electrons increases
(D) no effect
Q.57 In a photoelectric experiment, electrons are ejected from metals X and Y by light of intensity I and
frequency f. The potential difference V required to stop the electrons is measured for various frequencies.
If Y has a greater work function than X ; which one of the following graphs best illustrates the expected
results?
(A) (B) (C) (D)
Q.58 An image of the sun is formed by a lens of focal-length of 30 cm on the metal surface of a photo-electric
cell and a photo-electric current I is produced. The lens forming the image is then replaced by another of
the same diameter but of focal length 15 cm. The photo-electric current in this case is
(A) I/2 (B) I (C) 2I (D) 4I
Q.59 Monochromatic light with a frequency well above the cutoff frequency is incident on the emitter in a
photoelectric effect apparatus. The frequency of the light is then doubled while the intensity is kept
constant. How does this affect the photoelectric current?
(A) The photoelectric current will increase.
(B) The photoelectric current will decrease.
(C) The photoelectric current will remain the same.
(D) None of these
Q.60 In the experiment on photoelectric effect using light having frequency greater than the threshold frequency,
the photocurrent will certainly increase when
(A) Anode voltage is increased
(B) Area of cathode surface is increased
(C) Intensity of incident light is increased
(D) Distance between anode and cathode is increased.
10
Q.61 If a parallel beam of light having intensity I is incident normally on a perfectly reflecting surface, the force
exerted on the surface, equals F (Assume that the cross section of beam remains constant). When the
surface is held at an angle , the force is
(A) 2F tan (B) F cos (C) F cos2 (D) 2F
Q.62 A proton and an electron are accelerated by same potential difference starting from rest have de-Broglie
wavelength p and e.
(A) e = p (B)e < p (C) e > p (D) none of these.
Q.63 An electron with initial kinetic energy of 100 eV is accelerated through a potential difference of 50 V.
Now the de-Broglie wavelength of electron becomes
(A) 1 Å (B) 5.1 Å (C) 3 Å (D) 12.27 Å
Q.64 If h is Planck’s constant is SI system, the momentum of a photon of wavelength 0.01 Å is:
(A) 10–2 h (B) h (C) 102 h (D) 1012 h
Q.65 Let K1 be the maximum kinetic energy of photoelectrons emitted by a light of wavelength 1 and K2
corresponding to 2. If 1 = 22 , then :
(A) 2K1 = K2 (B) K1 = 2K2 (C) K1 < 2
K2(D) K1 > 2K2
11
ANSWER AND SOLUTION
Q.1 (D)
Sol. B = 2
3
'R
I
42R
I
400
=
'R
3
R
1
8
I0(x)
Q.2 (A)
Sol. B
=
40
3r
rV
=
40
2r
sinqV
= 10–7 × 22
º30sin1002 = 25 × 10–7 T = 2.5 T
Q.3 (A)
Sol. kBjBiBB zyx
B = 2z
2y
2x BBB
since Bx = B
y = B
z so B = 3 B
0
B = 3 ·
40
= R
I2 = 3 R2
I0
Q.4 (A)
Sol. Bx =
40
1
11
R
IN2
Bx = 4 × 10–4 (E)
N
S
EW
x
y
By =
40
2
22
R
IN2 = 9 × 10–4 (W)
B = 5 × 10–4 west
Q.5 (A)
Sol. B = r2
I
40
× +
r
I
40
× =
r4
I0
1
2
1 =
8
3
r
I0
Q.6 (B)
Sol. B1 =
40
a
I(sin + sin ) =
40
º30cosa2
º30sin2I
B
= kBkBkBkBB 4321
+ .....
=
40
º30cosa
º30sin2Ik –
40
º30cosa2
º30sin2Ik +
40
º30cosa3
º30sin2Ik + .....
=
40 k
a3
I2 –
40
a32
I2k +
40 k
a33
I2 + .....
=
40
a3
I2
.....
4
1
3
1
2
11 k
= a34
I20
log
e (1 + 1) k +
a34
I20
log
e 4 k
12
Q.7 (C)
Sol.21P BBB
BP =
y
I2
410
+
x
I2
420
x
y
p(x,y)I2
I1
0 =
x
I2
4y
I2
42010
y = 2
1
I
Ix
Q.8 (A)
Sol.d
x = sin 45º x =
2
d
we can extend wire and then subtract the field of extended part.
B1 =
2/d
I
40
(sin 0º + sin 90º) –
2/d
I
40
(sin 0º + sin 45º)
90°
d
P
45°
x=
d
I2
40
2
11 =
d22
I0
2
11
B1 ,
B
2 B = (B1 + B
2) = 2B
1 = d2
I0
2
11
Q.9 (A)
Sol.21 BBB
)i(4
I2
a4j
a
I2
4B 00
X
ii
i
(0, 0 – a)
ZY
=
40
a
I2)ji(
Q.10 (C)
Sol. B =
)xd2(
)I4(2
4x
I2
400
=
40
2I
)xd2(
4
x
1
x
4I
y
I
(–d,0,0) (d,0,0)
(2d-x)
P
For B to be minimum dx
dB = 0 x =
3
d2
13
Q.11 (A)
Sol. dI = 2
Id
Field at centre due to very long wire carrying current dI
d
dI
dB =
d
R
I
4R
I
2 200
BdB
=
2/
0
2/
0
jcosdBicosdB
= R
I
R4 20
2/
0
2/
0
jdsinidcos
]ji[R
I
R4B
20
B = 2R
I
R4 20
Q.12 (A)
Sol. Field due to one conducts is B,
By Ampere circuit law
Idl.B 0
s
B1 ×
2
d2 =
0J ×
2
2
d
=
4
dJ0
Vacuum
A
d
B = 2B1 = 2
dJ0 =
20
2dJ
Q.13 (B)Sol. Speed will be increased due to electric field only
2V0 = 2
02x VV
Vx = 3 V
0 V
x = U
x + a
xt
3 V0 = - + m
qEt t =
qE
mV3 0
Q.14 (D)
Sol. eE = 1
20
r
mV r
1 =
eE
mV20
eV0B =
2
20
r
mV r
2 =
eB
mV20
2
1
r
r =
E
BV0
14
Q.15 (D)
Sol. eE = 1
20
r
mV r1 =
eE
mV20
eV0 B = 2
20
r
mV r2 =
eB
mV0
2
1
r
r =
E
Bv0
Q.16 (B)
Sol. R d qB
mVd V
m
Bqd V
max =
m
Bqd
Q.17 (A)
Sol. Fe = 2
2
r
Kq =
0r
1
2
2
r
q F
m =
40
2
221
r
Vqq =
40
2
22
r
Vq
2
2
200m
e
V
C
V
1·
1
F
F
Q.18 (B)
Sol. r = qB
mE2 r
q
m
2
16:
1
4:
1
1:r:rr 2OHeH = 1 : 2 : 2
Q.19 (C)
Sol. r = qB
mT2
qB
mv
r' = )B3(q
)T2(m2 =
3
2r
9
2R
Q.20 (C)
Sol. 0FF me
Fe = F
m eE = eVB
v = B
E 3
5
102
102.3
= 1.6 × 108 m/s
r = 319
83
102106.1
106.1101.9
qB
mv
= 0.45m
Q.21 (A)
Sol. )VB(e)BV(e)BV(qFm
)j3i4( × 10–13 = 16 × 10–19 )jBiB( yx × 2.5 × 107 k
)j3i4( = )jB40iB40( xy j1.0i075.0B
15
Q.22 (B)
Sol. r = qB
mv r v
Q.23 (A)
Sol. T = qB
m2
Q.24 (B)
Sol. )BV(eF
Force will be along BO, or unti vector = –2
)ji(
Q.25 (B)
Sol. Pitch = V cos × T = V cos× qB
m2 = 3
Q.26 (B)Sol. Since it will have force only of electric field, so locus will be straight line.
Q.27 (C)Sol. Work done electric field = K
qE0x
0 =
2
1mv2
x0 =
2
1
0
2
qE
mv
j3i4V
V = 5 From (1) and (2) x0 =
0E2
25
Q.28 (C)Sol. Taking motion along y axis (con by electric field)
= y0 = u
yt +
2
1q
yt2
0 = 0 – vt + 2
1
m
qEt2
y
V
EB,
xu
t = qE
mv2... (1)
In this time charge must complete one or more revolution in x – z plane due to magnetic field
T = qB
m2 = –2 t = nt ... (2)
qE
mv2 = n ×
qB
m2 n =
E
vB
16
Q.29 (A)
Sol. From condition one and two we find that magnetic field is in k . In third situation field and v are in same
direction force will be zero.
]nBi2[ej2 ]nBi[ej n = – k
Q.30 (D)
Sol. T1 =
qB
M2T
2 =
qB
)M2(2 T
2 =
qB
M4
they will meet again when first will complete two revolution and second will complete one revolution sodirection.
d = v cost = v cos.2 qB
)M2( =
qB
cosMv4
Q.31 (C)Sol. Block will loses confact when force due to magnetic field will become equal to mg cosqVB = mg cos
qB
cosmgV
= g sint =
qB
cotm
Q.32 (D)
Sol. dF = 2Isin2
IdlB = T.IR B = T
dF
/2T cos /2T cos /2
/2 dl
sin/2
B
/2T = IRBT = 100 × 0.5 × 0.2T = 10N
Q.33 (A)
Sol. F =
40
d
II2 21
F = l
d
222
40
2A
2A
F' = 4
F
d
112
40
l
Q.34 (A)Sol. = i
iAB = I
iR2B = 2
1MR2
B
i
= M
iB2 =
2
1042 = 40 rad/s2
17
Q.35 (A)Sol. mg = kx
mg + ILB = k.2xFrom (1) and (2)
ILB = mg B = IL
mg
B = EL
mgR
Q.36 (B)
Sol. y2 = 2x = 2 × 2 y = ± 2 & j4L
)BL(IF
= 2 ]k4j4[ = 32 )kj( = 32 i
Q.37 (B)Sol. = NIAB sin
= 2n.2I.2aB sin30º = 2n.2I.2aB cos60º
B60°
30°A
= 4nIab cos60º
Q.38 (B)
Sol. )B(IF
force will be towards Q.
Q.39 (A)Sol. A real vects will be to the plane area vectos is at 60º angle with x axis and 30º angle with –z axis.
ANIM
22 mAmp1010M
M
= 0.1 Amp -m2
kº30cosMi60cosMkMyiMxM
M
= 0.05 )k3i(
Q.40 (A)
Sol. yB
z
V cos
V sin
(0, 0)
Negative z coordinatex
18
Q.41 (C)Sol. Pr = Pb
r
r hc
t
n
= b
b hc
t
n
b
r
b
r
n
n
> 1
Q.42 (B)
Sol./hc
P e = i
e)12400(
10 3–
(5000)(e) = 0.16 × 10–6
= 50
1241016.0 3– = 0.4 × 10–3 = 0.04%
Q.43 (D)
Sol. K =
hc –
K' = 4/3
hc
– =
hc
3
4 – =
hc
3
4 –
3
4 +
3
= 3
4
–
hc +
3
=
3
4K +
3
Q.44 (C)
Sol. Vs = e
–h
V's = e
–)2(h =
e
)–h(2 = 2VS +
e
Q.45 (B)
Sol. KEmax = eV 4 eV V= 4
Q.46 (A)
Sol. 10.4 + 1.7 = E = 12.1
Q.47 (A)
Sol. One photon corresponds to one electron
Q.48 (C)
Sol. KEmax = h –
KEmax = h(2) – = 2 (h – ) +
/hc
IA
dt
dv =
h
IA
dt
'dv =
)2(h
A)I2(
=
dt
dv
is = is
19
Q.49 (C)
Sol. Vs = e
–h = constant
Q.50 (D)
Sol. i =
dt
dve =
A
R4
P2 ×
h
1 × × e
i 2R
1
Q.51 (C)Sol. = h f0
hf1 = + KEmax KEmax = h1 – = h (1 – 0)
Q.52 (A)
Sol.
–5
–2
KE
KE
2
1
22
21
mv2
1
mv2
1
= 4
1
2
1
v
v =
2
1
Q.53 (C)
Sol. V = e
hc
=
e
hc –
e
V2 – V1 = e
hc
12
1–
1
Q.54 (B)Sol. 5 = + 2
= 3eV6 = f + KEmax KEmax = 3eV eVs = 3eV Vs = – 3V
Q.55 (B)
Sol. (KEmax)emitted =
–hc
= 200
1240 – 4.5 = 1.7 eV
(KEmax)reached = 1.7 + 2 = 3.7 eV
Q.56 (B)
Sol. KEmax = hv –
dt
dn =
h
IA
20
Q.57 (A)Sol. hf – = eV (f0)y > (f0)x
Q.58 (B)Sol. Photo electric current depends only upon total no. of photons incident. It is independent the area over
which the photons are incident changing the fecal length results in changes in are only
Q.59 (B)
Sol. i = eh
IA
i' =
)2(h
IAe i' < i
Q.60 (C, D)
Sol. i = eh
IA
Increase in either of intensity or area will result in inerease in photo current
Q.61 (C)
Sol. F = c
IA2
F' = c
cosIA2 2 = F cos2
Q.62 (C)
Sol. = p
h =
mK2
h =
mqV2
h
p
e
=
e
e
m
m e > p
Q.63 (A)Sol. KE = 100 + 50 = 150 ev
= )KE(m2
h = 19–31–
34–
106.1150101.92
106.6
= 1Aº
Q.64 (D)
Sol. p =
h = 12–10
h = 1012 h
Q.65 (C)
Sol. K1 = 1
hc
– =
22
hc
– K2 =
2
hc
–
K1 = 2
K2 – =
2
K2 –
2
