22.Draw a schematic ray diagram of reflecting telescope showing how
rays coming from a distant object are received at the eye-piece.
Write its two important advantages over a refracting telescope. [3]
Ans. The reflecting telescope makes use of a concave mirror as objective.
The rays of light coming from distant object are incident on the objective
(parabolic reflector). After reflection the rays of light meet at a point where
another convex mirror is placed. This mirror focusses light inside
the telescope tube. The final image is seen through the eyepiece.
The images produced by the reflecting telescope is very bright and its
resolving power is high
Advantages
(i) The resolving power (the ability to observe two objects distinctly) is high,
due to the largediameter of the objective.
(ii) There is no chromatic aberration as the objective is a mirror.
23. Meeta’s father was driving her to the school. At the traffic signal she
noticed that each traffic light was made of many tiny lights instead of a
single bulb. When Meeta asked this question toher father, he explained
the reason for this.
Answer the following questions based on above information:
(i) What were the values displayed by Meeta and her father?
(ii) What answer did Meeta’s father give?
(iii) What are the tiny lights in traffic signals called and how do these operate?
Ans. (i) Awareness for energy conservation, power saving and knowledge about traffic rules.
(ii) Meeta’s father said that these are LED light which consume less power and high reliability.
(iii) The tiny lights in traffic signols are LIGHT EMITTING DIODE.
These are operated by connecting the P–N Junction diode in forward biased condition.
OR
(i) Write the function of a transformer. State its principle of working with the help of a
diagram. Mention various every losses in this device.
(ii) The primary coil of an ideal step up transformer has 100 turns and transformation ratio
is also 100. The input voltage and power are respectively 220 V and 1100 W. Calculate
(a) number of turns in secondary
(b) current in primary
(c) voltage across secondary
(d) current in secondary
(e) power in secondary
Ans. (i) A transformer is an electrical device for converting an alternating
current at low voltage into that at high voltage or vice versa.
*. If it increases the input ac voltage, it is called step up transformer.
* .If it decreases the input ac voltage, it is called step down transformer.
Principle
It works on the principle of mutual induction i.e., when a changing current is passed
through one of the two inductively coupled coils, an induced emf is set up in the other coil.
