Answer
Verified
415.8k+ views
Hint : In order to solve this question, we are first of all going to compute the dot products of the vectors $ {e_0} $ and $ n $ , the vectors $ e $ and $ n $ , after that the former is subtracted from the latter and the relation which is obtained is further simplified according to the options given and the correct option is chosen.
The dot product of two unit vectors $ e $ and $ n $ having angle $ \theta $ between them is given by
$ e \cdot n = 1 \times 1 \times \cos \theta \\
\Rightarrow e \cdot n = \cos \theta \\ $
And if the vectors are in opposite direction, the angle taken between them is $ 180 - \theta $
Complete Step By Step Answer:
Let us consider that the angles between the vectors $ {e_0} $ and $ e $ ,
$ e $ and $ n $ be $ \theta $ each
This implies that the dot product of the vectors $ {e_0} $ and $ n $ will be
$ {e_0} \cdot n = 1 \times 1\cos \left( {180 - \theta } \right) \\
\Rightarrow {e_0} \cdot n = - \cos \theta \\ $
And the dot product for the unit vectors $ e $ and $ n $ will be
$ e \cdot n = 1 \times 1 \times \cos \theta \\
\Rightarrow e \cdot n = \cos \theta \\ $
Subtracting the above two cross products
We get
$ e \cdot n - {e_0} \cdot n = \cos \theta + \cos \theta = 2\cos \theta $
Further solving this expression, we get
$ n\left( {e - {e_0}} \right) = 2\cos \theta \\
n\left( {e - {e_0}} \right) = 2\left[ { - {e_0} \cdot n} \right] \\ $
Doing dot product with $ n $ on both the side
$ n\left( {e - {e_0}} \right) \cdot n = 2\left[ { - {e_0} \cdot n} \right] \cdot n \\
\Rightarrow e = {e_0} - 2\left( {{e_0} \cdot n} \right) \cdot n \\ $
So, option $ \left( A \right) $ is correct.
Note :
It is important to note that as the unit vectors are from the incident and reflected rays from a mirror, so they form equal angles with the normal, this fact has been used with much importance in this question. As the directions of the $ {e_0} $ and $ n $ vectors are opposite that is why the angle between them is taken as $ 180 - \theta $ .
The dot product of two unit vectors $ e $ and $ n $ having angle $ \theta $ between them is given by
$ e \cdot n = 1 \times 1 \times \cos \theta \\
\Rightarrow e \cdot n = \cos \theta \\ $
And if the vectors are in opposite direction, the angle taken between them is $ 180 - \theta $
Complete Step By Step Answer:
Let us consider that the angles between the vectors $ {e_0} $ and $ e $ ,
$ e $ and $ n $ be $ \theta $ each
This implies that the dot product of the vectors $ {e_0} $ and $ n $ will be
$ {e_0} \cdot n = 1 \times 1\cos \left( {180 - \theta } \right) \\
\Rightarrow {e_0} \cdot n = - \cos \theta \\ $
And the dot product for the unit vectors $ e $ and $ n $ will be
$ e \cdot n = 1 \times 1 \times \cos \theta \\
\Rightarrow e \cdot n = \cos \theta \\ $
Subtracting the above two cross products
We get
$ e \cdot n - {e_0} \cdot n = \cos \theta + \cos \theta = 2\cos \theta $
Further solving this expression, we get
$ n\left( {e - {e_0}} \right) = 2\cos \theta \\
n\left( {e - {e_0}} \right) = 2\left[ { - {e_0} \cdot n} \right] \\ $
Doing dot product with $ n $ on both the side
$ n\left( {e - {e_0}} \right) \cdot n = 2\left[ { - {e_0} \cdot n} \right] \cdot n \\
\Rightarrow e = {e_0} - 2\left( {{e_0} \cdot n} \right) \cdot n \\ $
So, option $ \left( A \right) $ is correct.
Note :
It is important to note that as the unit vectors are from the incident and reflected rays from a mirror, so they form equal angles with the normal, this fact has been used with much importance in this question. As the directions of the $ {e_0} $ and $ n $ vectors are opposite that is why the angle between them is taken as $ 180 - \theta $ .
Recently Updated Pages
Write the IUPAC name of the given compound class 11 chemistry CBSE
Write the IUPAC name of the given compound class 11 chemistry CBSE
Write the IUPAC name of the given compound class 11 chemistry CBSE
Write the IUPAC name of the given compound class 11 chemistry CBSE
Write the IUPAC name of the given compound class 11 chemistry CBSE
Write the IUPAC name of the given compound class 11 chemistry CBSE
Trending doubts
Fill the blanks with the suitable prepositions 1 The class 9 english CBSE
Which are the Top 10 Largest Countries of the World?
How do you graph the function fx 4x class 9 maths CBSE
Distinguish between the following Ferrous and nonferrous class 9 social science CBSE
The term ISWM refers to A Integrated Solid Waste Machine class 10 social science CBSE
The Equation xxx + 2 is Satisfied when x is Equal to Class 10 Maths
Difference between Prokaryotic cell and Eukaryotic class 11 biology CBSE
Which is the longest day and shortest night in the class 11 sst CBSE
In a democracy the final decisionmaking power rests class 11 social science CBSE