Reflecting Telescope

Q. What is telescope ?, how it works??what is its applications?what is its principle

Q.

Draw a labelled ray diagram of a refracting telescope. Define its magnifying power and write the expression for it.
Write two important limitations of a refracting telescope over a reflecting type telescope.

Q. A small telescope has an objective lens of focal length 140cm andan eyepiece of focal length 5.0cm. What is the magnifying power ofthe telescope for viewing distant objects when (a) the telescope is in normal adjustment (i.e., when the final imageis at infinity)? (b) the final image is formed at the least distance of distinct vision(25cm)?

Q. In an astronomical telescope in normal adjustment a straight black line of length $L$ is draw on inside part of objective lens. The eye-piece forms a real image of this line. The length of this image is $I$. The magnification of the telescope is

1. $\frac{L}{I}$
2. $\frac{L}{l}+1$
3. $\frac{L+I}{L-I}$
4. $\frac{L}{I}-I$

Q. In an electron microscope, electrons accelerated by a voltage of $50\text{kV}$ are used. In an optical microscope of the same aperture, yellow light of wavelength $5900\mathring{\text{A}}$ is used. The resolving power of the electron microscope will be $n$ times higher than that of the optical microscope, where $n$ is of the order of

1. ${10}^2$
2. ${10}^3$
3. ${10}^4$
4. ${10}^5$

Q. An astronomical telescope has a magnifying power $10$. The focal length of the eye piece is $20$ cm. The focal length of the objective is -

1. $200$ cm
2. $\left(\frac{1}{2}\right)\text{cm}$
3. $\left(\frac{1}{200}\right)\text{cm}$
4. $2$ cm

Q. (a) Draw a ray diagram showing the formation of image by a reflecting telescope.
(b) Write two advantages of a reflecting telescope over a refracting telescope.

Q. A telescope's objective diameter is 122 cm and light of 800 nm is used. If two stars at distance ${10}^8$ km are observed, what should be the minimum distance between them?

1. 80 km
2. 160 km
3. 200 km
4. 40 km

Q. Calculate the limit of resolution of a telescope objective having a diameter of $200\text{cm}$, if it has to detect light of wavelength $500\text{nm}$ coming from a star.

1. $610\times {10}^{-9}\text{radian}$
2. $152.5\times {10}^{-9}\text{radian}$
3. $457.5\times {10}^{-9}\text{radian}$
4. $305\times {10}^{-9}\text{radian}$

Q. Why reflecting type telescope is preferred over refracting type

Q. An astronomical telescope has a large aperture to

1. have high resolution.
2. increases thr span of observation.
3. have low dispersion
4. reduce spherical aberration

Q.

Why do we apply sign convention twice in lens, one time in the formula itself and also in the problems?Clear explanation required...

Q. What is the radius of curvature of an equiconvex lens made of glass of refractive index $\frac{5}{3},$ if its focal length in air is $40\text{cm}$ ?

1. $10\text{cm}$
2. $\frac{160}{3}\text{cm}$
3. $20\text{cm}$
4. $\frac{140}{3}\text{cm}$

Q. A thin biconvex converging lens of refractive index $1.5$ has power of $+5\text{D}$. When this lens is immersed in a liquid, it acts as a diverging lens of focal length $100\text{cm}$. The refractive index of the liquid is

1. $\frac{2}{3}$
2. $\frac{15}{11}$
3. $\frac{4}{3}$
4. $\frac{5}{3}$

Q.

A telescope of aperture diameter $5m$ is used to observe the moon from the earth. Distance between the moon and earth is $4\times {10}^{5}km$. The minimum distance between two points on the moon’s surface which can be resolved using this telescope is close to (Wavelength of light is $5500\stackrel{\circ }{A}$)

1. $60m$

2. $20m$

3. $600m$

4. $200m$

Q. If the reflected ray is rotated by an angle of 4 in clockwise direction then the mirror was rotated by (a) 2θ in anti-clockwise direction (b) 4θ in anti-clockwise direction (c) 2θ in clockwise direction (d) 4θ in clockwise direction

Q. An astronomical telescope has on objective of focal length $200cm$ and an eye piece of focal length $4.0cm$. The telescope is focused to see an object $10km$ from the objective. The final image is formed at infinity. Find the length of the tube and the angular magnification produced by the telescope.

1. $196cm,-50$
2. $204cm,-50$
3. $206cm,-50$
4. $200cm,-50$

Q. Two identical thin plano-convex lenses of refractive index $\mu$ are silvered, one on the plane side and the other on the convex side. The ratio of their focal lengths is

1. $\mu$
2. $\frac{\mu +1}{\mu }$
3. $\frac{\mu }{\mu -1}$
4. $\frac{\mu }{\mu +1}$

Q. An electron microscope uses electrons accelerated by a voltage of 50 kV. Determine the de-Broglie wavelength associated with the electrons. Taking other factors, such as numerical aperture etc., to be same, how does the resolving power of an electron microscope compare with that of an optical microscope which used yellow light?

Q. A point object at $O$ and a diverging lens is shown in the figure given below. Find the position of final image formed from $P$.

1. $-5\text{cm}$
2. $+10\text{cm}$
3. $-15\text{cm}$
4. $+20\text{cm}$

Q. What is a spherometer?

Q. Focal length of objective lens and eyepiece of an astronomical telescope are $100\text{cm}$ and $2\text{cm}$ respectively. Find the angular magnification produced in the case of normal adjustment:

1. $100$
2. $50$
3. $200$
4. $25$

Q. Magnifying power of a terrestrial telescope is $40$ in the case of normal adjustment. Find its maximum magnifying power, if focal length of eyepiece is $6.25\text{cm}$.

1. $46.25$
2. $50$
3. $44$
4. $48.25$

Q. Two thin converging lenses are placed on a common axis, so that the focus of the second lens coincides with the optic center of the first lens. An object is placed as shown. Find the lateral maginification of the system of lenses

1. $\frac{1}{2}$
2. $-\frac{1}{2}$
3. $\frac{1}{3}$
4. $\frac{2}{3}$

Q. A thin glass lens with relative refractive index ${\mu }_a^g=1.5$ , has an optical power of $-5\text{D}$ in air. Its optical power in a liquid medium with relative refractive index ${\mu }_a^l=1.6$ will be

[Assume, lens is fully immersed in the liquid]

1. $-\frac{5}{8}\text{D}$
2. $+\frac{5}{8}\text{D}$
3. $-\frac{8}{5}\text{D}$
4. $+\frac{8}{5}\text{D}$

Q. A astronomical telescope has objective and eyepiece of focal lengths $40cm$ and $4cm$ respectively. To view an object $200cm$ away from the objective, the lenses must be separated by a distance:

1. $54.0$ cm
2. $37.3$ cm
3. $46.0$ cm
4. $50.0$ cm

Q. (a) A giant refracting telescope at an observatory has an objective lens of focal length $15m$. If an eyepiece of focal length $1.0$ cm is used, what is the angular magnification of the telescope?
(b) If this telescope is used to view the moon, what is the diameter of the image of the moon formed by the objective lens? The diameter of the moon is $3.48\times {10}^{6}m$, and the radius of lunar orbit is $3.8\times {10}^{8}m$.

Q. A star, emitting a radiation of wavelength $5000\mathring{\text{A}}$, is approaching earth with a speed of $3\times {10}^6\text{m/s}$. The wavelength of the radiation received on earth will be,

1. $5100\mathring{\text{A}}$
2. $4900\mathring{\text{A}}$
3. $5050\mathring{\text{A}}$
4. $4950\mathring{\text{A}}$

Q.

Which Analysis Tool Was Invented by Xerox PARC?

Q. State any one advantage of using a reflecting telescope in place of a refracting telescope.