Concave Lens Questions
NCEA 2.3 Wave
This sim covers NCEA Level 2 Standard 2.3. Demonstrate understanding of Waves
1. Enter the answer in the "Your Answer" box on the right (all answers rounded to 3 significant figures).
2. Click the "Answer" button on the left.
3. Your answer, mark and steps will be displayed on the right, and recorded in the "Report" sheet.
4. Click the "New Question" button if you want to try again.
5. Click the "Reset All" button if you want to clear everything and start from the beginning.
6. The result of each attempt will be recorded. Please click "Report " to see your results.
7. The comments provided for each step gives the formula and explanation for solving the problem.
8. The comment given in "Note" provides the underlying assumption/theory of the question.
9. '*' indicates the difficulty level: * is easy, ** is medium, and *** is advanced.
Video Help: 3
Significant Figures
Question 1a-Image Position*
Leon is viewing an image with a lens.
The object is placed 6 cm away
from a CONCAVE Lens with a
focal length of 5 cm.
Video Help
What is the distance between the image and
the lens?
(Be careful; concave lenses have a
virtual focus. The focal length is negative
and the distance, di, will be too)
Your Answer
Solution
Mark
Step 1:
Step 2:
Note:
-2.73E+00
1 / (-5) = 1 / 6 + 1 / Di
1 / Di = -1 / 5 - 1 /6
1 / Di = 1 / -0.367
Di = -2.727
The negative sign implies that
the image is virtual and'
in this case, in front of the lens
Question 1b -Image Height *
The object is 6 cm High.
What is the height of the image?
Video Help
Your Answer
Solution
Mark
Step 1:
Step 2:
Step 3:
-2.73E+00
Hi / 6 = -2.727 / 6
Hi = 6 * -0.455
Hi = -2.727 (cm)
Question 1c - Nature*
What is the nature of the image
(is it virtual or real)?
Your Answer
Solution
Mark
Step:
(pick one)
Virtual
All images produced by a
concave lens are virtual,
upright and diminished
Video Help
Question 2a -Image Position*
Leon is viewing a second image.
The object is placed 4 cm away
from a CONCAVE Lens with a
focal length 6 cm.
Your Answer
Solution
Mark
Step 1:
Step 2:
What is the distance between the image and the lens?
Video Help
(Be careful; concave lenses have a
virtual focus. The focal length is negative
and the distance, di, will be too)
Note
-2.40E+00
1 / (-6) = 1 / 4 + 1 / Di
1 / Di = -1 / 6 - 1 /4
1 / Di = 1 / -0.417
Di = -2.4
The negative sign implies that
the image is virtual and,
in this case, in front of the lens
Question 2b - Image Height*
The object is 3 cm high
What is the height of the image?
Your Answer
Solution
Mark
Step 1:
Step 2:
Step 3:
-1.80E+00
Hi / 3 = -2.4 / 4
Hi = 3 * -0.6
Hi = -1.8 (cm)
Video Help
Question 2c - Nature*
What is the nature of the image
(is it virtual or real)?
Video Help
Your Answer
Solution
Mark
Step:
(pick one)
Virtual
All images produced by a
concave lens are virtual
whether it is before or after
the focal point
Question 3- Magnification Factor **
Leon is given another image.
The object is placed 8 cm from a concave lens
and gives an image reduction factor of 2.
Your Answer
Solution
Mark
Step 1:
What is the focal length of the lens?
Video Help
(Be careful; concave lenses have a
virtual focus. The focal length is negative
and the distance, di, will be too)
Step 2:
Because the image is virtual, the distance Di will be a
negative number, although this does not affect the value
calculated from the reduction factor
-2.67E+00
Remember Hi/Ho = Di/Do, so
Di / Do = 1/2
Di = (1/2) * 8 (Do)
Because the image is virtual Di is negative
1/f = 1/8(Do) - 1/4(Di)
f = -2.667