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Heat Energy that increases hotness of an object.  Temperature A reliable measure of the hotness of an object, is its temperature .  Thermometer A device used to measure temperature, is called thermometer .  Types of thermometer (i) Clinical thermometer (ii) Laboratory thermometer (iii) Maximum-minimum thermometer Clinical thermometer -The thermometer used to measure temperature of body, is called clinical thermometer.  -It consists of- glass tube,                           Bulb                           Mercury thread                           Kink -Range- 35°C to 42°C. -It has kink.  Clinical thermometer Laboratory thermometer -The thermometer used to measure temperature of an object, is called laboratory thermometer.  -It consists of- glass tube,                           Bulb                           Mercury thread                            -Range- -10°C to 110°C. -It doesn't have kink.  Maximu

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

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

Reaching the Age of Adolescene  Adolescene The period of life, when the body undergoes changes , leading to reproductive maturity, is called adolescene.  Period - age of 11 to age of 19. Also called " teen age ". Because this period covers the teen ages i.e, 13 to 19  Adolescene may begin earlier in girls than boys.  Puberty Period during adolescene, when human body undergoes several changes, is called puberty.  Important change - Boys and girls become capable of reproduction.  Changes at puberty   Increase in height  Change in body shape  Change in voice  Increased activity of sweat and sebaceous glands  Development of sex organs  Reaching mental, intellectual and emotional maturity Changes in Girls   Increase in height Region below the waist becomes wider  Less growth of muscles  Voice becomes high pitched.  Increased activity of sweat and sebaceous glands Ovaries enlarge.  Eggs begin to mature.  Reaching mental, intellectual and emotional maturity Changes in boys   Increa

Combustion and Flame  * Combustion - - Combustion is a chemical process. - In combustion, substance reacts with oxygen. - Heat is given off.    Substance + Oxygen ----> Heat - Example- Burning of paper or Magnesium * Combustible substance or fuel - - The substance that undergoes combustion, is called combustible substance . - Example- Paper. * Non-combustible substance - - The substance that doesn't undergo combustion, is called non-combustible substance. - Example- Stone * Ignition temperature Lowest temperature at which  a substance catches fire is called its ignition temperature. * Ignition temperature of wood is greater than that of kerosene. So, kerosene burns first and wood later. Lower ignition temperature -----> Burns faster. * Conditions necessary for combustion (a) Combustible substance - -Substance that can be burnt. -Example- Paper (b) Combusting Substance -Substance that helps in combustion, i.e. oxygen. (c) Ignition temperature

Materials: Metals and Non-metals * Lustre -    Lustre is physical property of substance by    which it looks shiny. * Malleability -    Malleability is property of metal, by which    they can be beaten into thin sheets. * Ductility -    Property of metal, by which they can be    drawn into wires, is called ductility. * Good conductor of heat/electricity    -The materials through which heat/electricity    can pass, is called good conductor of    heat/electricity.    -Example- Iron. * Poor conductor of heat/electricity    -The materials through which heat/electricity      cannot pass, is called poor conductor of      heat/electricity.    - Example- Plastic * Sonorous -    Metals are sonorous since they produce    ringing sound. * Physical properties of metals and Non-    metals    - Metals are lustrous. Non-metals are      non-lustrous.    - Metals are hard. Non-metals are soft.    - Metals are solid. Non-metals are liquid or      gas.    - Metals ar

  Synthetic Fibres and Plastic-                   Summary         NCERT CBSE CLASS 8 SCIENCE * Fibres -        -Very thin thread        - Thread is prepared from it. * Fibres ----> Thread/Yarn---->Fabric/Cloth---->             ---->Dress * Types of Fibres -      (a) Natural fibres -       -Fibres that are obtained from plants or         animals, is called natural fibres.       -Examples- Cotton, Jute, Silk, Wool      (b) Artificial/Synthetic fibres-        -Fibres that are not obtained from plants         or animals, is called synthetic fibres.       -Examples- Rayon, Nylon, Acrylic,                            tericot etc., * Monomer - (Mono- Single, Mere- Part/Unit)      -Small Single unit whose repeatation make       a large single unit.      -Example- Paper is the monomer of book. * Polymer - (Poly- Many, Mere- Part/Unit)      -Large single unit which is formed from       small single units.      -Example- Book is the polymer of paper. *

Microorganisms- Our friend and Foe  NCERT CBSE CLASS VIII Science Chapter 2  This test contains 10 multiple choice questions each carrying 2 marks.  You have to fill your details first and then attempt answer.  After attempting answers, click on submit.  Don't forget to click on "view your score'' after submission of answers.  Best of luck.  Loading…

Microorganisms:Friends or Foe NCERT Class VIII chapter 2(Science)  Loading…