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Beam balance

We know, refractive index (RI) of a medium = (speed of light in the air)/(speed of light in the medium)

According to the problem, 3/2 = (3 x 10^8 m/s)/(speed of light in glass) 

Hence, speed of light in glass = (3 x 10^8 m/s)/(3/2) = 2 x 10^8 m/s .    (Ans.)

Submultiples means you have to tell smaller units of something. Here in this case smaller units of Kilogram can be: Gram (g) Decigram (dg) Milligram (mg) Micrograms (ug) and so on.

The shortest distance between initial and final point is called displacement.

Frictional force : opposes the relative motion between the contact surfaces of the objects. It is major necessity in our daily life such as writing on a paper(friction is present between the surface of pencil and paper through which it make possible to write) , friction facilitate us to walk , holding a glass of water,etc., These are all possible acts due to friction present. Friction can be acts as evil if we consider the amount of loss of energy in any process such as , the wear-and-tear of the tires of vehicles on the road during motion is due to friction, pushing of the heavy objects on the rough surface makes it difficult to move due to friction present. ★ So, overall we can say that friction is the necessary evil in the human life.

The factors affecting density of a substance are its mass, volume, physical state of matter and the ambient temperature.

Density of a substance is directly proportional to its mass. while inversely proportional to its volume and ambient temperature. Density of a substance also varies with the change in its physical state.

Answer:

 When a current carrying conductor is placed in a magnetic field,it experiences a force which produces a torque that rotates the conductor. This is because  any current carrying conductor will produce an electromagnetic field around it and so the magnetic field produced by the conductor will interact with the main magnetic field already present which exerts a force on the conductor. The direction of the force is readily given by Fleming's Left  hand rule 

Suppose the sides of the coil(conductor) are AA' and BB' and the direction of current in the coil is such that the current enters along AA' and leaves along BB'. Let us assume that the coil experiences a torque in a counter clockwise direction when the coil side AA' is under  North pole of the main field. After rotating through half turn, the coil side BB' comes under  North pole.But as the direction of current in BB' is opposite to that of AA',the torque now will be in clockwise direction and as a result no unidirectional torque will be produced to rotate the coil.

Now suppose the direction of current in the coil side BB' is reversed (and automatically in AA' is also reversed),when it comes under  North pole,the torque will again be counterclockwise. And after completion of full turn,the current in coil side AA' will again be reversed  when it comes under  North pole so that a unidirectional torque is produced and the coil continues to rotate  counter clockwise. This automatic reversal  of the current is accomplished by commutator and brush gear and so the DC motor rotates continuously.   

As 1 light year is the distance travelled by light in vacuum in one year therefore distance of quasar from earth is 3× 10^ 9 light years

We know that S.I unit of power lens 1dioptre,D= reciprocal of focal length(f) in metre So, D=1/f or, f=1/D=1/2= 0.5 metre= 50 c.m. So, focal length of this lens is = 50 c.m.

1Horse Power= 746 Watts