GOOD SOURCE OF ENERGY
A good source of energy is the one that:
CONVENTIONAL SOURCES OF ENERGY
IMPROVEMENTS IN THE TECHNOLOGY FOR USING CONVENTIONAL SOURCES OF ENERGY
ALTERNATIVE OR NON-CONVENTIONAL SOURCES OF ENERGY
CHAPTER 4 MAGNETIC EFFECTS OF CURRENT
Field lines are used to represent a magnetic field. A field line is the path along which a hypothetical free north pole would tend to move. If the field lines are closer, it means that the magnetic field is greater.
MAGNETIC FIELD DUE TO CURRENT
A metallic wire carrying an electric current has a magnetic field associated with it. The field lines about the wire consist of a series of concentric circles whose direction is given by the right-hand rule.
The right hand rule: If you are holding a current carrying conductor in your right hand such that the thumb points towards the direction of current, then you fingers will wrap around the conductor in the direction of the field lines of the magnetic field.
FORCE ON A CURRENT-CARRYING CONDUCTOR IN MAGNETIC FIELD
A current carrying current in a magnetic field experiences a force on it whose direction can be found out by Fleming’s left hand rule. According to this rule, stretch the thumb, forefinger and the middle finger of your left hand such that they are mutually perpendicular. If the first finger points in the direction of magnetic 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.
An electric motor is a rotating device that converts electrical energy to mechanical energy.
The changing magnetic field in a conductor induces a current in another conductor is called electromagnetic induction.
The direction of induced current in a conductor can be found out using Fleming’s right hand rule. If you stretch the thumb, forefinger and middle finger of right hand so that they are mutually perpendicular to each other, the forefinger indicates the direction of the magnetic field, the thumb shows the direction of motion of conductor and the middle finger shows the direction of the induced current.
In an electric generator, mechanical energy is used to rotate a conductor in a magnetic field to produce electricity.
DOMESTIC SUPPLY OF ELECTRICITTY
In our houses we receive AC electric power of 220 V with a frequency of 50 Hz. One of the wires in this supply is with red insulation, called live wire. The other one is of black insulation, which is a neutral wire. The potential difference between the two wires is 220 V. The third wire is the earth wire that has the green insulation and this is connected to a metallic body deep inside earth. It is used as a safety measure to ensure that any leakage of current to a metallic body does not give any severe shock to a user.
A fuse in a circuit prevents damage to the appliances and the circuit due to overloading. Overloading can occur when the live wire and the neutral wire come into direct contact or there is a fault in any appliance. In such a situation, the current in the circuit abruptly increases. This is called short-circuiting.
CHAPTER 2 THE HUMAN EYE AND THE COLOURFUL WORLD
THE HUMAN EYE
The human eye is like a camera. Light enter the light through a thin membrane called the cornea. It forms a transparent bulge on the front surface of the eyeball. Behind the cornea, the iris is present. The iris is a dark muscular diaphragm that controls the size of the pupil. The pupil regulates and controls the amount of light entering the eye. The eye lens forms an inverted real image of the object on the retina. The retina is a delicate member having enormous number of light sensitive cells. The light sensitive cells get activated upon illumination and generate electric signals. These signals are sent to the brain via the optic nerves. The brain interprets these signals and finally, processes the information.
POWER OF ACCOMODATION
The ability of the eye lens to adjust its focal length is called the power of accommodation. The change in the curvature of the eye lens can thus change its focal length. This modification in the curvature of the eye lens is done by the ciliary muscles.
The smallest distance at which the eye can see objects clearly without strain is called the near point of the eye or the least distance of distinct vision. For a young adult with normal vision, it is about 25cm.
DEFECTS OF VISION
The common refractive defects of vision include myopia, hypermetropia and presbyopia.
Myopia is also called short-sightedness. This happens when the image of distant objects is focussed before the retina. This defect is corrected by using a concave lens of suitable power.
Hypermetropia is also called far-sightedness. This happens when the image of nearby objects is focussed beyond the retina. This defect is corrected by using a convex lens of suitable power.
Presbyopia is when the eye loses the power of accommodation with age. It happens due to the gradual weakening of the ciliary muscles and diminishing flexibility of the eye lens.
DISPERSION OF LIGHT
The splitting of white light into its component colours is called dispersion. White light is composed of seven colours- Violet, Indigo, Blue, Green, Yellow, Orange and Red. The acronym used for these colours is VIBGYOR.
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