81. Who discovered the law of refraction of light?
a) Ibn al-Haytham
b) Johannes Kepler
c) Isaac Newton
d) Galileo Galilei
Answer: a) Ibn al-Haytham
82. Who invented the first successful helicopter?
a) Igor Sikorsky
b) Leonardo da Vinci
c) Gottlieb Daimler
d) Samuel Pierpont Langley
Answer: a) Igor Sikorsky
83. Who discovered the principles of radioactivity?
a) Marie Curie
b) Henri Becquerel
c) Ernest Rutherford
d) Max Planck
Answer: b) Henri Becquerel
84. Who invented the first practical steamboat?
a) Robert Fulton
b) James Watt
c) Thomas Newcomen
d) George Stephenson
Answer: a) Robert Fulton
85. Who discovered the laws of thermodynamics?
a) Sadi Carnot
b) Lord Kelvin
c) James Joule
d) Rudolf Clausius
Answer: a) Sadi Carnot