incl alt txt

book/demos/demo01/demo01.md

@@ -64,6 +64,7 @@ Cut one of the eggs in a bowl, fill the syringe with its contents, remove the ai
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+alt: an unboiled egg in shell in jar with vinegar
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 An unboiled egg in vinegar.
 ```
@@ -82,6 +83,7 @@ Together, decide which other substances you want to test (include some food colo
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+alt: unboiled egg without its shell in hands of experimenter
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 Unboiled egg without its shell.
 ```
@@ -112,6 +114,7 @@ What causes some substances to pass through both membranes, others to pass throu
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+alt: open egg, egg white is colored, inner part is still yellow.
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 Food coloring penetrates the outer but not the inner membrane.
 ```

book/demos/demo02/demo02.md

@@ -29,6 +29,7 @@ A cup of cappuccino is prepared by adding about 50 mL frothing, foaming milk to
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+alt: a cappuccino where the milk foam is clearly visible.
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 The context of this demonstration: A cappuccino
 ```
@@ -76,6 +77,7 @@ Steam can cause bad burns. So watch out with the steam coming through the rubber
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+alt: a bunsenburner heating the water in a flask, a connected tube to heat the milk.
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 The experimental setup
 ```

book/demos/demo03/demo03.md

@@ -49,6 +49,7 @@ Light the candle and put it under the vacuum bell jar so that smoke is trapped b
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+alt: left laser, center a vacuum bell jar.
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 The setup consisting of a laser, a vacuum bell jar and a small candle for smoke.
 ```
@@ -62,6 +63,7 @@ Turn the laser on and ask students what they observe. *Is the laser beam visible
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+alt: a red laser beam is visible inside the jar
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 The laser beam is well visible, but the entire bell jar is illuminated as well!
 ```
@@ -71,6 +73,7 @@ Ask students to write down their observation when you turn on the vacuum pump. I
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+alt: only two laser spots, at the corner of the jar, are visible
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 When the bell jar gets more and more vacuum, the light intensity of the laser beam is less until it is not visible at all anymore.
 ```

book/demos/demo04/demo04.md

@@ -23,6 +23,7 @@
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+alt: stacked blocks
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 A challenge: Building a slanting tower where the top block is not above the bottom block.
 ```
@@ -39,6 +40,7 @@ If you put two blocks on top of each other, then the upper one remains stable if
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 name: demo04_fig1
+alt: stacked blocks, evenly spaced.
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 The demo requires only some blocks.
 ```
@@ -52,6 +54,7 @@ Is it possible that the back of the top block passes the front of the bottom blo
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 name: demo04_fig2
+alt: schematic of stacked blocks illustrating how top one is left of the lowest one
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 We can try to use the approach that first comes into mind... but probably won't succeed.
 ```
@@ -67,6 +70,7 @@ It is also possible to arrange the pile in reversed order: from top to bottom ({
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 name: demo04_fig5
+alt: finger used to balance two block
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 Building the pile in reversed order requires to find the center of mass each time.
 ```
@@ -83,6 +87,7 @@ All of that above block 5 and the overhang is already more than one block length
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 name: demo04_fig3
+alt: schematic of correct way of stacking blocks
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 The physics (and mathematics) behind stacking blocks
 ```
@@ -96,6 +101,7 @@ The physics (and mathematics) behind stacking blocks
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 name: demo04_fig4
+alt: picture of the market hall in rotterdam, illustrating the practical use of stacked blocks
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 The market hall in Rotterdam is stacked according to the principle above. Figure obtained from: <a href="https://commons.wikimedia.org/wiki/File:Markthal-Rotterdam.jpg" target="_blank">https://commons.wikimedia.org/wiki/File:Markthal-Rotterdam.jpg</a> (CC BY-SA)
 ```

book/demos/demo05/demo05.md

@@ -28,6 +28,7 @@ In their own practical work students may easily overlook the details in the phen
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 name: demo05_fig1
+alt: setup, left a weight with string attached through wheels connected to spring-balance to cart to spring balance
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 A schematic of the experimental setup
 ```
@@ -56,6 +57,7 @@ A [Predict-Observe-Explain](../../Pedagogy/PoE.md) approach is appropriate here.
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+alt: the experimental setup as used in class
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 The actual setup
 ```

book/demos/demo06/demo06.md

@@ -24,6 +24,7 @@
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+alt: illuminated aquarium and a rainbow at the wall
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 An aquarium filled with water is put on an overheadprojector 
 ``` 
@@ -47,6 +48,7 @@ Cover the OHP with white sheets of paper. Put the container with water (about ¾
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 name: demo06_fig3
+alt: aquarium and two rainbows
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 The aquarium is slightly rotated resulting in two spectacular spectra.
 ``` 
@@ -56,6 +58,7 @@ The aquarium is slightly rotated resulting in two spectacular spectra.
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 name: demo06_fig4
+alt: light rays
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 The light rays move from A, B and C to A', B' and C'.
 ``` 
@@ -64,6 +67,7 @@ The light rays move from A, B and C to A', B' and C'.
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+alt: the setup, an aquarium on top of an overheadprojector
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 The setup. The rainbows appear on the left and right walls.
 ``` 

book/demos/demo07/demo07.md

@@ -27,6 +27,7 @@ Five or six pendulums are suspended from a rod ({numref}`Figure {number} <demo07
 width: 40%
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 name: demo07_fig1
+alt: horizontal rod, vertical strings of different lengths with balls
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 A rod with some balls suspended using strings.
 ``` 
@@ -44,6 +45,7 @@ Drill a narrow hole through each ball and through the broom stick. The string ca
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 name: demo07_fig2
+alt: experimenter demonstrating
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 The red ball starts to move.
 ``` 

book/demos/demo08/demo08.md

@@ -46,6 +46,7 @@ In this demonstration metal balls change into ping-pong balls. Of course that is
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+alt: three iron balls on top of box with corn
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 Balls before the transformation
 ```
@@ -63,6 +64,7 @@ Put the metal balls on top of the corn, then put the lid on the container and 
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 name: demo08_fig2
+alt: three white balls on top of box with corn
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 Balls after the transformation
 ```

book/demos/demo09/demo09.md

@@ -27,6 +27,7 @@ Just above the bubbling surface of boiling water, nothing unusual seems to be ha
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+alt: boiling water and a small tealight which is lit
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 The required materials
 ```
@@ -60,6 +61,7 @@ Bring the burning candle down into the kettle, and note that the flame dies. Sum
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+alt: tealight in the cooker
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 *left:* Above the kettle, the flame burns somewhat weaker.\
 *right:* Inside the kettle, above the water, the flame extinguishes

book/demos/demo10/demo10.md

@@ -24,6 +24,7 @@
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+alt: soap bubbles above a Van de Graaff generator
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 The soap bubble gun and the Van de Graaff generator. In this picture, most bubbles move away from the generator. 
 ```
@@ -46,6 +47,7 @@ Blow the bubbles from above to the Van de Graaff generator (or let a student do
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+alt: soap bubbles above a Van de Graaff generator
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 The bubbles on the left move towards the Van de Graaff generator, while the bubbles on the right move away from the generator. How is that possible?
 ```
@@ -59,6 +61,7 @@ Then you start the process of developing explanations and testing these using (b
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+alt: a cartoon with four different statements to express what is happening
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 The concept cartoon can be used to start the discussion.
 ```

book/demos/demo11/demo11.md

@@ -48,6 +48,7 @@ Think how the visibility of observations can be maximized. For example, put a ch
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 name: demo11_fig1
+alt: a turning rod with dices on it at the right but at the left dices are above the rod 
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 Are some of the dices falling faster than $g$?
 ```