Magnetic Field due to a Current through a Straight Conductor

1. Magnetic Field due to a Current through a Straight Conductor

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(a) Nature of magnetic field: The magnetic field lines due to a straight current carrying

conductor forms a pattern of concentric circles with their centers on the wire. These

concentric circles become larger & larger as we move away from it.

(b) The direction of this field can be found by Right hand thumb rule, which states that: If

a straight current carrying wire is imagined to be held in the right hand, with the thumb

stretched along the direction of current, then the direction of the magnetic field produced

by the current is in the direction in which the fingers are curled.

(c) If the current in the wire increases then the needle of the compass needle placed at that

point gets deflected by a larger angle.

The strength of magnetic field at a point due to this current carrying conductor is directly

proportional to the current. It means the strength of magnetic field increases with increase

in the value of current.

(d) The strength of magnetic field is inversely proportional to the distance. This means that

the strength of the magnetic field reduces with distance from the wire.

(e) If we reverse the direction of current in the straight conductor then the direction of

deflection of needle of compass also reverses.

Fleming’s 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 current, then the thumb will point in the direction of
motion or the force acting on the conductor.

The Human Eye Structure.

                                         The Human Eye Structure



*RETINA-- The eye lens system forms an image on a light-sensitive
screen called the retina.
*CORNEA-- Light enters the eye through a thin membrane called the cornea.
It forms the transparent bulge on the front surface of the eyeball
Most of the refraction for the light rays entering the eye occurs at the
outer surface of the cornea.
*EYE LENS-- The crystalline lens merely provides the finer adjustment of focal length
required to focus objects at different distances on the retina.
*IRIS-- Iris is a dark muscular diaphragm that controls the size of the pupil.
*PUPIL--- Pupil regulates and controls the amount of light amount of light entering
the eye.
*CILIARY MUSCLES---
When the muscles are relaxed, the lens becomes thin. Thus its focal length
increases. This enables us to see distant objects clearly.
When we are looking at objects closer to the eye, the ciliary muscles contract.
This increases the curvature of the eye lens. The eye lens then
becomes thicker. Consequently, the focal length of the eye lens decreases
This enables us to see nearby objects clearly
.
*OPTICAL NERVES--- The retina is a delicate membrane having enormous number of
light-sensitive cells. The light-sensitive cells get activated upon
illumination and generate electrical signals. These signals are
sent to the brain via the optic nerves. The brain interprets these
signals, and finally, processes the information so that we
perceive objects as they are.
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