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NCERT Based Test: Motion in Combined Electric & Magnetic Fields


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15 Questions MCQ Test Physics Class 12 | NCERT Based Test: Motion in Combined Electric & Magnetic Fields

NCERT Based Test: Motion in Combined Electric & Magnetic Fields for NEET 2023 is part of Physics Class 12 preparation. The NCERT Based Test: Motion in Combined Electric & Magnetic Fields questions and answers have been prepared according to the NEET exam syllabus.The NCERT Based Test: Motion in Combined Electric & Magnetic Fields MCQs are made for NEET 2023 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests for NCERT Based Test: Motion in Combined Electric & Magnetic Fields below.
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NCERT Based Test: Motion in Combined Electric & Magnetic Fields - Question 1

A charged particle with charge q enters a region of constant, uniform and mutually orthogonal fields  with a velocity  perpendicular to both , and comes out without any change in its magnitude or direction. Then 

Detailed Solution for NCERT Based Test: Motion in Combined Electric & Magnetic Fields - Question 1

When  are perpendicular and velocity has no change then qE = qvB i.e. v= E/B. The two forces oppose each other so, v is along  i.e., .
As  are perpendicular to each other 

NCERT Based Test: Motion in Combined Electric & Magnetic Fields - Question 2

A charged particle would continue to move with a constant velocity in a region wherein, which of the following conditions is not correct?

NCERT Based Test: Motion in Combined Electric & Magnetic Fields - Question 3

The cyclotron frequency vc is given by 

Detailed Solution for NCERT Based Test: Motion in Combined Electric & Magnetic Fields - Question 3

In cyclotron the centripetal force is balanced by magnetic force, then
qvB = mn2/r ⇒ qBr/m = v
where v = 2πrv∴ vc = qB/2πm

NCERT Based Test: Motion in Combined Electric & Magnetic Fields - Question 4

A charged particle is moving in a cyclotron, what effect on the radius of path of this charged particle will occur when the frequency of the radio frequency field is doubled?

Detailed Solution for NCERT Based Test: Motion in Combined Electric & Magnetic Fields - Question 4

As frequency of revolution in a cyclotron
vC = Bq/2πm is independent of r.
So the radius of path in the dees will remain unchanged. When the frequency is changed.

NCERT Based Test: Motion in Combined Electric & Magnetic Fields - Question 5

A cubical region of space is filled with some uniform electric and magnetic field. An electron enters the cube across one of its faces with velocity v and a positron enters via opposite face with velocity - v. At this instant, which one of the following is not correct?

NCERT Based Test: Motion in Combined Electric & Magnetic Fields - Question 6

A cyclotron is operated at an oscillator frequency of 12 MHz and has a dee radius R = 50 cm. What is the magnitude of the magnetic field needed for a proton to be accelerated in the cyclotron?

NCERT Based Test: Motion in Combined Electric & Magnetic Fields - Question 7

If an electron is moving in a magnetic field of 5.4 x 10-4 T on a circular path of radius 32 cm having a frequency of 2.5 MHz, then its speed will be 

Detailed Solution for NCERT Based Test: Motion in Combined Electric & Magnetic Fields - Question 7

Here, B = 5.4 x 10-4 T;
r = 32 cm = 32 x 10-2 m; v = 2.5 MHz = 2.5 x 106Hz 
The speed of electron on circular path
v = r x 2πv = 32 x 10-2 x 2 x 3.14 x 2.5 x 106
= 502.4 x 104 = 5.024 x 106 m s-1 

NCERT Based Test: Motion in Combined Electric & Magnetic Fields - Question 8

A proton and an α-partide enter in a unifoi magnetic field perpendicularly with same speed. The ratio of time periods of both particle (TP/Tα) will be

Detailed Solution for NCERT Based Test: Motion in Combined Electric & Magnetic Fields - Question 8

The time period of revolution of a charged particle in a magnetic field is 
T = 2πm/Bq
For proton, mP = m, qP = q ; ∴ TP = 2πm/Bq
Now, for α-particle, mα = 4m, qα = 2q
∴ Tα = (2π(4m))/(B(Bq)) = 2(2πm/Bq) ⇒ TP/Tα = 1/2

NCERT Based Test: Motion in Combined Electric & Magnetic Fields - Question 9

A proton, a deutron and an α-particle with same, kinetic energy enter perpendicularly in a uniform magnetic field, then the ratio of radii of their circular paths is

Detailed Solution for NCERT Based Test: Motion in Combined Electric & Magnetic Fields - Question 9

∵ r = ∴ r ∝ √m/q
Hence, rp : rd ; rα = 

NCERT Based Test: Motion in Combined Electric & Magnetic Fields - Question 10

If an electron enters with a velocity  into a cubical region in a uniform electromagnetic field and the orbit of the electron is found to spiral down inside the cube in plane parallel to x-y plane then the configuration of electric field and magnetic field is 

Detailed Solution for NCERT Based Test: Motion in Combined Electric & Magnetic Fields - Question 10

The orbit of the electron spirals down inside the cube in the plane parallel to x−y plane. Therefore  must be along +z  direction and should be along x−axis.

NCERT Based Test: Motion in Combined Electric & Magnetic Fields - Question 11

The energy of emergent protons in MeV from a cyclotron having radius of its dees 1.8 m and applied magnetic field 0.7T is (mass of proton = 1.67×10−27 kg):

Detailed Solution for NCERT Based Test: Motion in Combined Electric & Magnetic Fields - Question 11


= 1.22 x 10-11 j = 76 MeV

NCERT Based Test: Motion in Combined Electric & Magnetic Fields - Question 12

Which of the following is not correct about cyclotron?

Detailed Solution for NCERT Based Test: Motion in Combined Electric & Magnetic Fields - Question 12

The charged particles and ions in cyclotron can move along circular path only.

NCERT Based Test: Motion in Combined Electric & Magnetic Fields - Question 13

The operating magnetic field for accelerating protons in a cyclotron oscillator having frequency of 12 MHz is (q = 1.6 x 10-19C, mp = 1.67 x 10-27 kg and 1 MeV = 1.6 x 10-13 j)

Detailed Solution for NCERT Based Test: Motion in Combined Electric & Magnetic Fields - Question 13

NCERT Based Test: Motion in Combined Electric & Magnetic Fields - Question 14

In the question number 34, the kinetic energy (in MeV) of the proton beam produced by the accelerator is (radius of dees = 60 cm)

Detailed Solution for NCERT Based Test: Motion in Combined Electric & Magnetic Fields - Question 14

Final velocity of proton is 
v = r x 2πv = 0.6 x 2 x 3.14 x 12 x 106 = 4.5 x 107 m s-1

= 10.6 MeV

NCERT Based Test: Motion in Combined Electric & Magnetic Fields - Question 15

An electron is moving in a cyclotron at a speed of 3.2 x 107 m s-1 in a magnetic field of 5 x 10-4 T perpendicular to it. What is the frequency of this electron?
(q = 1.6 x 10-19 C, me = 9.1 x 10-31 kg)

Detailed Solution for NCERT Based Test: Motion in Combined Electric & Magnetic Fields - Question 15

v = 3.2 x 107 m s-1 ;B = 5 x 10-4 T
The frequency of electron is

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