Grade 10 Optics question

[ringelos]

I am having serious trouble with this question and I'm hoping to get some assistance with it. The question goes as follows:

 

Suppose a lens with a focal length of 10.0cm produces an inverted image half the size of a 4.0cm object. How far apart are the object and image? Show all your work.

 

Any help is appreciated.

[rktpro]

I am having serious trouble with this question and I'm hoping to get some assistance with it. The question goes as follows:

 

Suppose a lens with a focal length of 10.0cm produces an inverted image half the size of a 4.0cm object. How far apart are the object and image? Show all your work.

 

Any help is appreciated.

 

What you need to know is-

• Magnification
• The lens formula

Just a google for that.

[ringelos]

I think I have got to something.

 

From what I can tell, we have a hi=2 and a ho=4 and a focal length that doesnt fit into the equation.

Is this correct?

 

So m= 2/4 = -di/do

m= 0.5

 

If I am correct we now have magnification - now what?

Do we multiply our focal length by 0.5 to get a value, then add said value to our focal length?

 

So, 10x0.5 = 5, 10+5 = 15

[rktpro]

I think I have got to something.

 

From what I can tell, we have a hi=2 and a ho=4 and a focal length that doesnt fit into the equation.

Is this correct?

 

So m= 2/4 = -di/do

m= 0.5

 

If I am correct we now have magnification - now what?

Do we multiply our focal length by 0.5 to get a value, then add said value to our focal length?

 

So, 10x0.5 = 5, 10+5 = 15

 

Here it goes,

 

The focal length given is 10 cm. Because the lens has not been specified, it is obvious that focal length= +10cm and the lens is a convex lens.

Now you must know that, magnification=v/u= image height/object height. [hint: remember to use sign convention. Perpendicular distances downward to principle axis are negative]

Thus, say you get magnification=v/u= x. Now v = ux where x has some value.

 

Put this in 1/v-1/u=1/f , that is the lens formula.

Remember to use sign convention where ever you plug values.