PHYSICS

 Ans: Step down transformer. Secondary coil is made with thicker wire than primary coil wire. It means that more current is flowing through secondary coil. It indicates that secondary emf is lower than primary emf. Hence stepdown transformer 

Step up transformer increases the magnitude of alternating e.m.f.  As the power remains same , current should decrease as per the formula, power= emf x current. So the statement is TRUE.

Magnification is -5:  The negative magnification means the image is real and the absolute value(without negative sign) of magnification (5) indicates that the image is real and inverted.

In uniform circular motion,  1. Speed is constant. 2. Velocity is variable and acts along tangential direction  at a point. 3. Centripetal Force and acceleration act along the radius towards the centre if the circular path.  4. Centrifugal force appears to  act radially outwards. It is a virtual  ,fictitious force, not a real force.

Heat capacity depends on mass. More the mass of a substance, more is the heat capacity. That's why the cooking vessels have thick bases to absorb more heat and to tranfer more heat to the food for longer period of time.

 Any two masses in the universe attract each other with a force which is  i) directly proportional to the product of the masses, ii) inversely proportional to the square of the distance between their centres. F=GmM/r²  where G= universal gravitational constant. m and M are the masses of two bodies. r = distance between them.  * Larger the masses , greater is the force between them. * Larger the distance , smaller is the force. * If the distance is halved , force increases 4 times. * If the distance is doubled,  force becomes one-fourth. * The force is not effected with any medium between the masses. 

Q: What is the angle of deviation produced by a parallel glass slab? Ans: 0°. The incident ray is parallel to the emergent ray.

 Class 10                                                                     Marks: 20 Physics Revision ATTEMPT ALL QUESTIONS. Define moment of force. Write relationship between the SI and CGS unit of moment of couple. 2 Find the mass of the scale in equilibrium .                                          Draw diagrams and locate the centre of gravity  of hollow cone and triangular sheet. 2  State the  type of work done by a coolie  when i)  he lifts a load up ii) when he moves on a horizontal platform carrying load on his head.     2 A force is applied on a body of mass 20kg movong with a velocity of 40 m/s. The body attains a velocity of 50 m/s in 2  s. C...

 Red colour has longest wavelength so it has maximum speed in a medium compared to other colours.  As it travels with maximum speed in a medium,  the refractive index of the medium for Red colour is minimum.

Which is always constant for a machine of given design: MA or VR ? Ans: VR remains constant for a machine of given design as it depends on the distances moved by the load and effort but MA can vary due to the friction developed between the moving parts of the machine.

LENZ'S LAW is based on law of conservation of a) mass b) charge c) momentum  d) energy. Ans: d)   energy 

 Q: Why is uniform circular motion an accelerated motion? A: The velocity of  Uniform Circular motion changes continuously due to its changing direction. As there is change in velocity, the motion is accelerated motion.

  Question : Why are door handles fitted at the edge of the door ? Answer : Door handles are fitted at the edge to increase  the perpendicular distance of the force from the axis of rotation so that the minimum force can be applied to achieve the given torque.

 Q: Fog/ cloud appears white. Why ? Ans: Light is scattered by the fog particles. As the size of the particles is bigger than the wavelength of light, all colours are scattered to equal extent giving back white light.  The property of light responsible for white clouds: scattering of light.

 Convex lens can behave as a concave lens and vice versa when the lens is placed in a medium with refractive index more than that of the lens. Convex lens diverges and concave converges the rays.

Ans:  The replica of an object  formed by the intersection of reflected rays is called an image. Image is formed when the reflected rays actually meet at a point        ( real image)or appear to meet( virtual image)

 ABSOLUTE  REFRACTIVE INDEX  The absolute refractive index of a medium is the ratio of speed of light in vacuum and the speed of light in the medium. Absolute refractive index = Speed of light in vacuum or air                                                     Speed of light in the medium  For example, A.r.i of glass = speed of light in vacuum/speed of light in glass  3×10⁸/2×10⁸= 3/2=1.5 Its value is equal or more than 1. For vacuum or air, its value is 1. So its minimum value is 1. RELATIVE REFRACTIVE INDEX  The relative refractive index of a medium (a) with respect to another medium (b) is the ratio of speed of light in medium (b) and the speed of light in medium (a). Relative refractive index of  (a) wrt (b)=Speed of light in medium (b )                        ...

 Answer:  Inner pulleys are smaller than others to eradicate the frictional force between the ropes and inner pulleys while in use.

Spanner has a long handle. Why? Answer: When perpendicular distance between the force and the axis of rotation is large, smaller force is required to produce  the desired torque.