8.1 & 8.2

In 1895, a German physicist discovered that an unknown ray could pass through most substances and left shadow behind. He named the ray X-ray. He then captured the first X-ray image of his wife. His discovery was widely used in medical field. He did not patent his discovery and obtain the first Nobel Prize in Physics. Who is he?

• Wilhelm Roentgen

• Henri Becquerel

• Pierre Curie

• Isaac Newton

For his discovery of radioactivity, Henri Bacquerel was awarded Nobel Prize of Physics in 1903. What is the S.I. unit of radioactivity?

• Curie

• Moles

• Bacquerel

• Radac

Radioactivity is due to _______

• unstable nucleus

• unstable electron

• unstable proton

• unstable neutron

When a nucleus become very big, it become unstable. The nuclear force holding the atomic nuclei together cannot counterbalance the repulsive electromagnetic force between nucleus. Uranium-238 emits helium particle and become more stable Thorium-234 particle. What type of radiation is this?

• (α) alpha radiation

• (β) beta radiation

• (γ) gamma ray

• X-ray

What is the definition of half life?

• Time taken for the number of undecayed nuclei to be reduced to half of its original number(value)

• Time taken for the number of undecayed nuclei to be increased by two times of its original number(value).

• Ratio of number of undecayed nuclei to original number of nuclei after half a year.

• Total amount of radioactive emitted when the number of undecayed nuclei reduced to half in half a year.

Above shows the graph of count rate versus time of an radioactive material. Based on the graph, what will be the half life (T_1/2) of this material?

• 10 days

• 20 days

• 30 days

• 40 days

Which of the following is correct regards of the electrical charges of electron, proton and neutron?

"-" = negatively charge

"+"= positively charge

"x"= neutral

• Electron "-" ; Proton "+", Neutron "x"

• Electron "+" ; Proton "-", Neutron "x"

• Electron "-" ; Proton "x", Neutron "+"

• Electron "x" ; Proton "-", Neutron "+"

When an atom gains/losses electron, it becomes ion. Based on the table above, which of the following is an ion?

• P

• Q

• R

• S