Film: 9087

Science | 1960 | Sound | Colour


Sir Lawrence Bragg (Nobel prize winner, jointly with his father W.H.Bragg, Physics, 1915, for their work on the analysis of crystal structure by X-rays), gives a lecture at the Royal Institute. In 1965, Lord Bowden, who was then Minister of State in the Department of Education and Science, expressed a wish that the lectures given by Sir Lawrence Bragg be recorded in the form of films. The series Sir Lawrence Bragg at the Royal Institute is a result of his interest.

Sir Lawrence Bragg has a series of apparatus in front of him. Close up of Sir Lawrence Bragg's face, he announces that the lecture is about the three states of matter: solid, liquid and gas. Sir Lawrence Bragg points to a block of ice which represents the solid state of water and he also points to a flask full of water, a kettle is boiling steam escapes (gas state of water). Steam is visible because it condenses. Close up of Sir Lawrence Bragg surrounded by steam. An assistant hands Sir Lawrence Bragg a red hot poker which he plunges into the ice block. Close up of the red hot poker melting the ice and turning it into steam. Sir Lawrence Bragg places a circular perspex sheet in front of the steam, thus condensing the steam into water. Sir Lawrence Bragg shows the camera a pot containing liquid air, he pours liquid air onto the table and it runs on the table as if the table was red hot. Close up the liquid air running on the table. He holds a brass ball which has been cooling down in liquid air and places it into the flask containing liquid water, the ball makes a fizzy noise and turns into ice, he hammers the iced ball onto the table to crack the ice. Close up of Sir Lawrence Bragg saying that the change of state is due to the temperature. He picks up a steel ball and talks about the importance of atoms in matter. Close up of the steel ball held in his hand.

Sir Lawrence Bragg places himself in the line of the optical beam, the lights are dimmed, he holds a brown glass in front of his face in order to see the image that passed through the single slit. When the second slit is uncovered, can see fine black and white fringes. Sir Lawrence Bragg talks about Young's fringes and why scientists were so reluctant to believe in the wave theory of light. The assistant casts a very fine light source onto a screen, he then places his arm in front of the light source so that a shadow is cast. Close up of the shadow to show how sharp the details are (this sharpness puzzled early scientists a lot). The lights are turned up. Sir Lawrence Bragg explains that the reason the shadows are so sharp is because the wavelength of the light is very short compared to the size of the object casting the shadow, but if the waves are long compared to the size of the object (example, sound waves), as they pass the object, the waves seem to heal themselves. Close up of a sharp shadow being generated behind an obstacle and another close up that demonstrates that long waves heal themselves, thus the object casts no shadow. The lights are turned up. A lantern with a very thin slit is shun onto a plate with a window with an extended fine edge (the light will bend round the edge), the edge is replaced with a sewing needle, the light also bends around the needle. Sir Lawrence Bragg observes light bending around corners. Close up to show that the light is bending right into the shadow. Close up to show that light also bends around the sewing needle (fringes indicate that light bends round the corner). (Sir Lawrence Bragg reproduced the experiments that Thomas Young did at the Royal Institute in the early 1800's, he established the undulatory theory of light, he also discovered the principle of interference of light.)

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