the image of an object formed by a mirror is real inverted and is magnification -1. if the image is at the distance of 30 cm from the mirror where is the object placed find the position of the image if the object is now moved 20cm towards the mirror what is the nature of the image obtained justify your answer with the help of a ray diagram

Respuesta :

The nature of the image is magnified , virtual , and upright.

Further explanation

We will solve this problem using following formula:

[tex]\large{ \boxed {\frac{1}{s_o} + \frac{1}{s_i} = \frac{1}{f}}}[/tex]

where:

so = distance of object from mirror

si = distance of image from mirror

f = focal length of mirror

[tex]\texttt{ }[/tex]

Given:

Magnification = M = 1

Initial Image Distance = si = 30 cm

Difference of Object's Distance = Δso = 20 cm

Unknown:

Final Image Distance = si' = ?

Solution:

Initial Condition:

[tex]M = \frac{s_i}{s_o}[/tex]

[tex]1 = \frac{s_i}{s_o}[/tex]

[tex]s_i = s_o[/tex]

[tex]s_o = 30 cm[/tex]

[tex]\texttt{ }[/tex]

[tex]\frac{1}{s_o} + \frac{1}{s_i} = \frac{1}{f}[/tex]

[tex]\frac{1}{s_o} + \frac{1}{s_o} = \frac{1}{f}[/tex]

[tex]\frac{2}{s_o} = \frac{1}{f}[/tex]

[tex]f = \frac{1}{2} s_o[/tex]

[tex]f = \frac{1}{2} \times 30[/tex]

[tex]f = 15 \texttt{ cm}[/tex]

[tex]\texttt{ }[/tex]

Final Condition:

[tex]s_o' = s_o - \Delta s[/tex]

[tex]s_o' = 30 - 20[/tex]

[tex]s_o' = 10 \texttt{ cm}[/tex]

[tex]\texttt{ }[/tex]

[tex]\frac{1}{s_o'} + \frac{1}{s_i'} = \frac{1}{f}[/tex]

[tex]\frac{1}{10} + \frac{1}{s_i'} = \frac{1}{15}[/tex]

[tex]\frac{1}{s_i'} = \frac{1}{15} - \frac{1}{10}[/tex]

[tex]\frac{1}{s_i'} = \frac{2}{30} - \frac{3}{30}[/tex]

[tex]\frac{1}{s_i'} = -\frac{1}{30}[/tex]

[tex]s_i' = 30 \texttt{ cm}[/tex]

Because si' < 0 , the nature of the image will be magnified , virtual , and upright.

[tex]\texttt{ }[/tex]

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Answer details

Grade: High School

Subject: Physics

Chapter: Light

Keywords: Light , Mirror , Magnification , Ray , Diagram , Image , Real , Virtual

Ver imagen johanrusli

The final image formed after shifting the object will be virtualand erect image and formed at a distance of [tex]\boxed{30\,{\text{cm}}}[/tex] behind the mirror.

Further Explanation:

Given:

The magnification of the image for the object placed at [tex]30\text{cm}[/tex] from the mirror is [tex]-1[/tex].

The final distance of the object from the mirror is [tex]30\,{\text{cm}} - 20\,{\text{cm}} = 10\,{\text{cm}}[/tex] .

Concept:

The magnification of the image for the object placed at [tex]30\text{cm}[/tex] from the mirror is [tex]-1[/tex].

The magnification of the image can be represented as.

 [tex]m = - \dfrac{{{d_i}}}{{{d_o}}}[/tex]

Substitute [tex]-1[/tex] for [tex]m[/tex] and [tex]-30\text{cm}[/tex] for [tex]{d_o}[/tex] in above expression.

 [tex]\begin{aligned}- 1 &= - \frac{{{d_i}}}{{ - 30}}\\{d_i} &= - 30\,{\text{cm}}\\\end{aligned}[/tex]

Here, the image distance is equal to the object distance. In case of the mirror, the image distance and the object distance are equal only when the object is placed at the centre of curvature of the mirror.

Therefore, the focal length of the mirror will be half of the distance of the object from the mirror.

[tex]\begin{aligned}f&= \frac{{{d_o}}}{2}\\&= \frac{{ - 30}}{2}\,{\text{cm}}\\&= - {\text{15}}\,{\text{cm}}\\\end{aligned}[/tex]  

Now, the object is shifted towards the mirror. The new distance of the object from the mirror is [tex]10\text{cm}[/tex].

The mirror’s formula can be expressed as.

 [tex]\dfrac{1}{{{d_i}}} + \dfrac{1}{{{d_o}}} = \dfrac{1}{f}[/tex]

Substitute [tex]-10\text{cm}[/tex] for [tex]d_o[/tex] and [tex]-15\text{cm}[/tex] for [tex]f[/tex] in above equation.

 [tex]\begin{aligned}\frac{1}{{{d_i}}} + \frac{1}{{ - 10}} &= \frac{1}{{ - 15}}\\\frac{1}{{{d_i}}} &= \frac{1}{{10}} - \frac{1}{{15}}\\{d_i} &= 30\,{\text{cm}}\\\end{aligned}[/tex]

The image distance is positive. It means that the final image of the object will be formed behind the mirror i.e. the image will be virtual.

The magnification of the image is.

 [tex]\begin{aligned}m&= - \frac{{{d_i}}}{{{d_o}}}\\&= - \frac{{30}}{{ - 10}}\\ &= + 3\\\end{aligned}[/tex]

Thus, the image formed will be erect, virtual and three times the size of the object.

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Answer Details:

Grade: Middle School

Chapter: Mirror’s Formula

Subject: Physics

Keywords:  Image distance, object distance, mirror’s formula, magnification, 30 cm from the mirror, now moved 20cm, ray diagram, real inverted.

Ver imagen AkshayG