CognitoQuiz

Stars and Solar System Celestial objects The stars, the planets, the moons and many other objects in the sky are called celestial objects.  Full Moon Day  The day on which the whole disc of the moon is visible is known as full moon day.  New Moon Day On the fifteenth day after full moon day, the moon is not visible. This day is known as new moon day.  Crescent Moon  The moon whose only a small portion appears in the sky, is called crescent moon.  Phases of Moon  The various shapes of the bright part of the moon as seen during a month are called phases of moon.  The moon doesn't produce its own light.  We see the moon because, the sunlight falling on it gets reflected towards us.  The moon rotates on its axis.  The moon revolve around the Earth.  The moon has no atmosphere, no water,  Star The sun is also a star.  Sun appears larger than other stars. Because- -Stars are millions of times farther away than the sun.  Stars are not visible during day time. Because of the bright sunligh

What Makes Things Visible   When light from an object enters our eyes, then we see the object.  The light may have been emitted or reflected by the object.  Mirror   Highly polished surface is called mirror.  Reflection Bending back of light ray after falling on a surface, is called reflection.  Incident ray The light ray which strikes any surface, is called incident ray.  Reflected ray  The ray that comes back from the surface after reflection, is called as reflected ray.  Normal Line perpendicular to surface at point of incidence of light ray, is called normal.  Angle of incidence The angle between normal and incident ray, is called angle of incidence.  Angle of reflection The angle between normal and reflected ray, is called angle of reflection.  Laws of reflection (i) The incident ray, the normal at the point of incidence and the reflected ray, all lie in the same plane.  (ii) The angle of incidence is always equal to the angle of reflection.  Nature of Images formed by Plane Mirro

When we take off clothes in dark, we see a spark and crackling sound. Because - Our body gets rubbed with clothes.  - This produces charges.  - When charges meet, they cause spark and crackling sound.  Charged object Object having electric charge.  Example- Rubbed balloon Electric charges are generated by rubbing.  Types of charges-  (a) Positive charge  (b) Negative charge  Interaction between charges -Like charges repel each other.  -Unlike charges attract each other.  It is a convention to call the charge acquired by a glass rod when it is rubbed with silk as positive.  The another kind of charge is said to be negative.  Static charge  Charge that do not move.  Electric current Movement of charges , is electric current.  Electroscope  A device that test whether an object is charged or not, is called electroscope. 

Good Conductor The substance through which electricity can pass is called good conductor.  Examples - Copper, Aluminum Poor conductor The substance through which electricity can not pass is called poor conductor. Examples - Rubber, plastic etc.  Tester A device that test conductance of a substance, is called tester.  Solutions of acids, bases and salts are generally good conductor.  Chemical effects of Current Chemical reactions (effects) caused when electricity passes through a conducting liquid, is chemical effects of current.  How to recognize chemical reaction - Release of gas - Change of colour of solution - Release of heat - Formation of new substance In battery No. of terminals- 2 (positive and negative)  Positive terminal is also called Anode .  Negative terminal is also called cathode .  Solution  is called electrolyte .  Passing current through a solution What happens when electricity is passed through c

Friction The force that opposes the relative motion between two surfaces in contact, is called friction.  Factors affecting friction Weight of object  Nature of surfaces in contact More the weight of object, more the friction.  More smooth surface experience less friction.  Importance of friction Friction helps in stopping object Friction helps to write, walk,  Friction helps in all activities Friction produces heat.  Harm cause by Friction Sole of shoes wear out.  Machine parts get wear out.  Friction can be increased by making surfaces rough. ( More rough means more interlocking between surfaces which means more friction )  Friction can be decreased by applying lubricant on surfaces.  Friction can be decresed by changing shape of object.  Rolling friction The force that oppose motion of rolling object, is rolling friction.  Sliding friction The force that oppose motion of sliding object, is sliding friction.  Sliding fri

Force   The push or pull of an object, is called force.  Forces are due to interaction between objects.  Force applied on an object in the same direction add to each other.  Force applied on an object in opposite directions substract each other.  The strength of force is measured by its magnitude.  A force can change the state of motion of an object.  Change in state of motion jeans Rest to motion Motion to rest  Increase in speed  Decrease in speed Force on an object may change its shape.  Types of forces   Contact force   The force that can be applied only by touching object,is called contact force.  Non-Contact force   The force that can be applied without touching object,is called contact force.  Muscular force   The force resulting due to action of muscles is called muscular force.  Friction The force that oppose motion of an object.  Magnetic force The force exerted by a magnetic material is called magnetic force.  Like pole repel each other.  Unlike pole attract each other.  Ele