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Fleming's left hand rule - class-XII

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An electron having a charge e moves with a velocity v in X-direction. A magnetic field acts on it in Y-direction. The force on the electron acts in

  1. positive direction of Y-axis

  2. negative direction of Y-axis

  3. positive direction of Z-axis

  4. negative direction of Z-axis


Correct Option: D
Explanation:
As electron moving in positive x-direction, so the current  is moving in negative x-direction ( the direction of your middle finger) and the magnetic field acts on positive Y-direction ( the direction of your index finger) then thumb will be in negative Z-direction which is the direction of force. 

A positively charged particle falls vertically downwards. The horizontal component of earths magnetic field will deflect it towards

  1. West

  2. East

  3. South

  4. North


Correct Option: B

You are sitting in a room in which a strong magnetic field is directed from your left towards right. A beam of electrons is directed from front towards you. What would be the direction of magnetic force on this beam ?

  1. downwards.

  2. upwards.

  3. towards right 

  4. towards left 


Correct Option: A
Explanation:
The direction of the magnetic field is from left to right, the direction of the beam of electrons is from your front hence the direction of the current is from back to front. Now by applying Fleming left hand rule we can find that the direction of the magnetic force on the beam of electron is downwards.

An electron is travelling along the x-direction. It encounters a magnetic field in the ydirection. Its subsequent motion will be

  1. straight line along the x-direction

  2. a circle in the zx-plane

  3. a circle in the yz-plane

  4. a circle in the xy-plane


Correct Option: B
Explanation:

The magnetic force acting on a charged particle is given by 

$\vec{F}=q(\vec{v}\times \vec{B})$
Hence direction of force acting one electron is $\hat{i}\times \hat{j}=\hat{k}$
The force experienced is in z-direction. So the particle moves in the zx plane.

An electric current runs counterclockwise in a rectangular loop around the outside edge of the page which lies flat on your table. A uniform magnetic field is then turned on directed parallel to the page from the top to bottom. The magnetic force on the page will cause:

  1. the left edge to lift up

  2. the right edge to lift up

  3. the top edge to lift up

  4. the bottom edge to lift up


Correct Option: C
Explanation:

Current is flowing anticlockwise in the rectangular loop and in the upper edge of page current is flowing towards left and magnetic field is from top to bottom , so by applying Fleming's left hand rule the direction of force is found to be in the upward direction, lifting the top edge up.

A positive charge is at rest in a uniform magnetic field directed to the right. What force does the positive charge feel, due to the magnetic field?

  1. An upward force.

  2. A downward force.

  3. A force to the left.

  4. No force is felt.


Correct Option: D
Explanation:
For experiencing a magnetic force on a charge  particle, the particle should move in the magnetic field with some velocity. As the velocity of the particle is zero so, the force on the particle is also zero.

The direction of force on a current carrying conductor placed in a magnetic field is given by :

  1. Fleming's Left Hand Rule

  2. Fleming's Right Hand Rule

  3. End Rule

  4. Right Hand Palm Rule


Correct Option: A
Explanation:

The direction of this force is always right angles to the plane containing both the conductor and the magnetic field, and is predicted by Fleming’s Left-Hand Rule.

A vertical wire carries a current in upward direction. An electron beam sent horizontally towards the wire will be deflected (gravity free space) :

  1. towards right

  2. towards left

  3. upwards

  4. downwards


Correct Option: C
Explanation:

$F= q(\vec{v} \times \vec{B})= (-e)( -v\hat{i}\times (-B\hat{k}))=evB\hat{j}$
Thus, force on the electron beam is along the +ve y-axis.

In _______ Fleming Left hand rule is not used.

  1. Electric fan

  2. Mixer

  3. Computer

  4. Electric generator


Correct Option: D

Fleming's left hand rule is used to find

  1. Direction of magnetic field 

  2. Direction of current

  3. Direction of magnetic force acting on conductor

  4. None of these


Correct Option: A

An electron is moving vertically downwards at any place. The direction of magnetic force acting on it due to horizontal component of earth's magnetic field will be

  1. towards east

  2. towards west

  3. towards north

  4. towards south


Correct Option: B
Explanation:

According to Fleming left hand rule, if the direction of horizontal component of earth's magnetic field is from south to north and direction of velocity of electron is downwards then the direction of the force given by the thumb is towards west.

An electron and a proton travel with equal speeds and in the same direction, at $90^o$ to a uniform magnetic field. They experience forces which are initially

  1. in opposite direction and differ by a factor of about 1840

  2. in the same direction and differ by a factor of about 1840

  3. equal in magnitude but in opposite directions

  4. identical


Correct Option: C
Explanation:
As both of the particle having same speed and in the same field at same angle, they will be experiencing same force but in opposite direction as they are opposite in charge. 

How will be the direction of force will get changed, if the current is reversed in the conductor placed in a magnetic field?

  1. Direction of force rotates by right angle

  2. Direction of force is reversed.

  3. Direction of force remains same

  4. Can't say


Correct Option: B

A proton is projected horizontally eastward in a uniform magnetic field, which is horizontal and southward in direction. The proton will be deflected

  1. upward

  2. downward

  3. northward

  4. southward


Correct Option: B
Explanation:

By Fleming's left hand rule, taking velocity (middle finger) in east direction and magnetic field (index finger) in south direction, we get force (thumb) in vertically downward direction.

An electron enters a magnetic field at right angles to it. The direction of force acting on the electron will be

  1. to the right.

  2. to the left.

  3. out of the page.

  4. into the page.


Correct Option: D

Which rule determines the direction of force experienced by a current Carrying straight conductor placed in a magnetic field which is perpendicular to it.

  1. Maxwell right hand grip rule

  2. Fleming's left hand rule

  3. Fleming's right hand rule

  4. None


Correct Option: B
Explanation:

We considered the direction of the current and that of the magnetic field perpendicular to each other and found that the force is perpendicular to both of them. The three directions can be illustrated through a simple rule, called Flemings left-hand rule. According to this rule, stretch the thumb, forefinger and middle finger of your left hand such that they are mutually perpendicular. If the first finger points in the direction of magnetic field and the second finger in the direction of the current, then the thumb will point in the direction of motion or the force acting on the conductor.

In the statement of Fleming's left hand rule, magnetic field is represented by

  1. thumb

  2. fore finger

  3. middle finger

  4. none


Correct Option: B
Explanation:

The direction of the current and that of the magnetic field perpendicular to each other and found that the force is perpendicular to both of them. The three directions can be illustrated through a simple rule, called Flemings left-hand rule. According to this rule, stretch the thumb, forefinger and middle finger of your left hand such that they are mutually perpendicular. If the first finger points in the direction of magnetic field and the second finger in the direction of the current, then the thumb will point in the direction of motion or the force acting on the conductor.

In the statement of Fleming's left hand rule, what do the direction of centre finger represents

  1. motion

  2. magnetic field

  3. current

  4. none


Correct Option: C
Explanation:

The direction of the current and that of the magnetic field perpendicular to each other and found that the force is perpendicular to both of them. The three directions can be illustrated through a simple rule, called Flemings left-hand rule. According to this rule, stretch the thumb, forefinger and middle finger of your left hand such that they are mutually perpendicular. If the first finger points in the direction of magnetic field and the second finger in the direction of the current, then the thumb will point in the direction of motion or the force acting on the conductor.

In the statement of Fleming's left hand rule, force acting on the conductor is  is represented by

  1. thumb

  2. fore finger

  3. middle finger

  4. none


Correct Option: A
Explanation:

The direction of the current and that of the magnetic field perpendicular to each other and found that the force is perpendicular to both of them. The three directions can be illustrated through a simple rule, called Flemings left-hand rule. According to this rule, stretch the thumb, forefinger and middle finger of your left hand such that they are mutually perpendicular. If the first finger points in the direction of magnetic field and the second finger in the direction of the current, then the thumb will point in the direction of motion or the force acting on the conductor.

An electron is moving towards east in a magnetic field acting vertically downwards. So the electron is deflected towards:

  1. South 

  2. North

  3. East

  4. West


Correct Option: A
Explanation:

An electron is moving towards east in a magnetic field acting vertically downwards. So, the electron is deflected in a mutually perpendicular direction to magnetic field. Using Fleming's left hand rule it is in south direction .

Fleming's left-hand rule is used to find the direction of _______ acting on the current carrying conductor placed in a/an ________ field.

  1. Force, Magnetic

  2. Force , Electric

  3. Torque, Magnetic

  4. Torque, Electric


Correct Option: A

At an instant a charge q moves with a velocity of 5 m/s along y-axis in a uniform magnetic filed $\underset{B}{\rightarrow}=(2\widehat{i}+3\widehat{j}+4\widehat{k})$

  1. The charge will experience a force in xy plane

  2. The charge will experience a force in yz plane

  3. The charge will experience a force in zx plane

  4. The charge will experience a force along x-axis


Correct Option: C

A charge particle is moving in the direction of a magnetic filed.The magnetic force acting on the particle:

  1. is in the direction of its velocity

  2. is in the direction opposite to its velocity

  3. is perpendicular to its velocity

  4. is zero


Correct Option: D

According to Fleming's left hand rule,whose direction is indicated by thumb?

  1. $ Electric current O $

  2. $ Magnetic force O $

  3. $ Magnetic field O $

  4. $ None of these O $


Correct Option: C
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