Help and Instructions for using the Curved Mirror apps

The Curved Mirror apps enable you to experiment with the optics of concave, convex and parabolic mirrors. The procedure for exploration is:

• Set a focal length and click on "Draw Mirrror".

• Once the mirror is drawn, click at a point on the canvas. The coordinates of the selected point will be displayed in the middle window. Once you are satisfied with the position shown, click on "Show object". All rays that will be drawn will start from this point.

• An incident ray always starts from the point selected above and moves towards the mirror at a specific angle with respect to the horizontal. This angle can be changed using the edit box (following the word "angle"). You can also change the colour of the ray by clicking on the coloured rectangle, which will take you to a colour selector. Click on the colour you want.

• Once you have set the colour and angle of the ray, click on "Draw Ray". The incident and the reflected ray will be drawn.

• Sometimes, especially for virtual images, it is useful to extend the reflected ray backwards. This can be done by checking the "With backward extension" checkbox.

• After drawing one ray, you can change the colour and/or the angle to draw a second ray from the same point. This will let you identify the image point for these two rays. Repeating the process with many rays will enable you to see how most of the rays meet at the same point after reflection, thereby forming an image. If the angle of the ray is large, you will notice that the ray may not pass through the same point as other rays do, a phenomenon called "aberration".

• You can also choose to draw a special ray, one that starts from the object and passes through the centre of curvature. This ray is normal to the mirror and is therefore reflected in the same direction.

• A quick way to draw multiple rays from the same point is to click on the "Automate" button. You can select the range of angles to be used as well as the step size between consecutive angles.

• The "Start Over" button cleans the entire canvas so that you can change parameters.