Tag: physics

Questions Related to physics

The mirror used by E.N.T. specialists is _____

physics reflection of light at curved surfaces uses of curved mirrors uses of spherical mirror uses of spherical mirrors

  1. Plane

  2. Concave

  3. Convex

  4. None of these

Show answer
Correct Option: B
Explanation:

The mirror used by E.N.T. specialists is concave mirror. 

Concave mirror concentrate all the rays at desired part which makes it bright.

In torches, search lights and headlights of vehicles the bulb is placed:

physics reflection of light at curved surfaces uses of curved mirrors uses of spherical mirror uses of spherical mirrors

  1. between the pole and the focus of the reflector

  2. very near to the focus of the reflector

  3. between the focus and centre of curvature of the reflector

  4. at the centre of curvature of the reflector

Show answer
Correct Option: B
Explanation:

In torches, search lights and headlights of vehicles the bulb is placed very near to the focus of the reflector to get a parallel beam of light through which we can see to a longer distance.

Magnification produced by a rear view mirror fitted in vehicles:

physics reflection of light at curved surfaces uses of curved mirrors uses of spherical mirror uses of spherical mirrors

  1. is less than one

  2. is more than one

  3. is equal to one

  4. can be more than or less than one depending upon the position of the object in front of it

Show answer
Correct Option: A
Explanation:

We know, magnification(M)$=\dfrac{\text {height  of  image}\ (h _i)}{\text{height  of  object}\ (h _o)}$
If the magnification will be 1 or more than 1, then the height of image will be equal or greater than the height of object. So, only a part of the image will be viewed through the possible aperture of the mirror. This situation will not provide the driver with the detailed idea of motion of vehicles following.
Hence, Magnification produced by a rear view mirror fitted in vehicles is less than one.

The concave mirrors are used in:

physics reflection of light at curved surfaces uses of curved mirrors uses of spherical mirror uses of spherical mirrors

  1. Reflecting telescope

  2. Magic-lanterns

  3. Cinema projectors

  4. All of these

Show answer
Correct Option: D
Explanation:

A reflecting telescope uses concave mirrors as they produce images similar to the images produced by convex lenses i.e. upright and smaller than the object.

The magic lantern used a concave mirror in back of a light source to direct as much of the light as possible through a small rectangular sheet of glass.

Concave mirrors project a beam of light outward, which is required in a cinema projector.

A concave mirror forms an image of the sun at a distance of 12 cm from it. Then:

physics reflection of light at curved surfaces uses of curved mirrors uses of spherical mirror uses of spherical mirrors

  1. the radius of curvature of this mirror is 6 cm

  2. to use it as a shaving mirror, it can be held at a distance of 8-10 cm from the face

  3. if an object is kept at a distance of 24 cm from it, the image formed will be of the same size as the object

  4. all the above alternatives are correct

Show answer
Correct Option: B,C
Explanation:

Concave mirror forms an image of the sun at a distance of 12 cm.
So the focal length of mirror is 12 cm.
Radius of mirror is $f \times 2=24cm$
For shaving we need to get a virtual image which should be magnified and erect.
So the mirror must be kept at a reasonable distance of 8-10 cm which is within focus and pole.
As the radius is 24cm the object placed at center forms image at the same place
Options $B,C$ are correct.

___________ are used in telescopes to reflect light.

physics reflection of light at curved surfaces uses of curved mirrors uses of spherical mirror uses of spherical mirrors

  1. Concave mirrors

  2. Convex mirrors

  3. Plane mirrors

  4. Convex lenses

Show answer
Correct Option: A
Explanation:

Concave mirrors are used in telescope to reflect light.


Answer-(A).

The light emanating from a torchlight is

physics reflection of light at curved surfaces uses of curved mirrors uses of spherical mirror uses of spherical mirrors

  1. Convergent

  2. Divergent

  3. Parallel

  4. Irregular

Show answer
Correct Option: B
Explanation:

A torch has a bulb working on a battery. A bulb spreads its light rays in all directions. Thus it always diverges.

Mirror used by a dental surgeon is ___________.

physics reflection of light at curved surfaces uses of curved mirrors uses of spherical mirror uses of spherical mirrors

  1. Plane

  2. Convex

  3. Concave

  4. Convex and concave

Show answer
Correct Option: C
Explanation:

The concave mirror is used by the dentist as the image formed by the concave mirror when placed between pole and focus is magnified and erect and it provides a clear image to repair tooth cavities.

If 0.5 of any substance is completely transformed into energy, then how much energy in kilo-joule will be obtained?

physics work and energy law of conservation of energy the law of conservation of energy types of energy

  1. $1.5\times 10^{10} kilo-joule$

  2. $3.0\times 10^{10} kilo-joule$

  3. $4.5\times 10^{10} kilo-joule$

  4. $6.0\times 10^{10} kilo-joule$

Show answer
Correct Option: C
Explanation:

Using $E=mc^2$
$m=0.5 g=5\times 10^{-4}kg$
$c=3\times 10^5m/s$
Hence, $E=5\times 10^{-4}\times (3\times 10^8)^2J$
$45\times 10^{12}J$
$=4.5\times 10^{10}kJ$

A domestic gas cylinder contains about 14.2 kg of LPG. A strong smelling substance called ethyl mercaptan is added to the LPG to detect the leakage of gas from the cylinder. On being lighted, it burs with a blue flame. One gram of LPG produces about 50 kJ of heat. Weight of the domestic cylinder is -

physics energy transformations and energy transfers law of conservation of energy the law of conservation of energy types of energy

  1. 142 N

  2. 152 N

  3. 132 N

  4. 122 N

Show answer
Correct Option: A