Slave work was very difficult. Most women cooked, cleaned the house and raised the children of their white masters. Men were trained to be carpenters or masons. Most of them, however, were farm labourers. They planted and harvested crops.

Not all Blacks in America were slaves. “Free Blacks” lived and worked in big American cities, but they had very few rights. Expressing political views, carrying guns and meeting with white people was forbidden.

Americans in the northern states thought that slavery shouldn’t be allowed in a free country. As time went on, more and more people joined in the fight to end slavery. These abolitionists helped slaves escape to the North through secret routes. This system was called the Underground Railway.

In 1860 Abraham Lincoln was elected President of the United States. He was strongly against slavery. Many southern states withdrew from the union and formed their own country – the Confederate States of America. It was the beginning of the Civil War, which lasted until 1865.

In 1863 Abraham Lincoln abolished slavery in the Emancipation Proclamation. The northern states won the Civil War and American slaves were free.

In the past, African Americans have been known by many names. They were called Negroes, Blacks, and Coloureds. In the last 30 years, the term African Americans has officially been used.

About half of them live in the southern states of the USA, the rest in large cities of the East, Midwest and West.

African Americans – % of total population (2010)
Source; U.S. Census Bureau
Image: Ghislain Montvernay ; Licence : CC BY-SA 3.0
via Wikimedia Commons

Image: Openclipart , Public Domain

Discovery

In 1895, a German scientist, Wilhelm Roentgen, discovered X-rays by accident. He called them X-rays because he hadn’t seen such a form of energy before. In mathematics X means something unknown. Roentgen took his first X-ray pictures of the bones of his hand. In 1901 he received the first Nobel Prize for Physics for his discovery.

X-rays in medicine

X-rays are valuable in medicine because they can see through certain parts of the body. Doctors can take pictures of bones, teeth and tissue. They use these pictures to see which bones are broken or to find out which teeth have holes in them.

To produce X-ray pictures you need two things: a special plate that can capture X-rays is placed behind a part of a person’s body. A machine that produces X-rays is put in front of the person.

The X-rays are strong enough to pass through the skin and muscles but they cannot pass through hard objects like bones. In the picture you see hard objects, like bones, as white areas. Objects that X-rays go through are dark.

X-ray of a hand
Image: Creazilla , Public Domain

There are some situations in which X-rays cannot give you a clear picture. Some organs, for example, may block X-rays from showing a broken bone. For this reason computed tomography (CT) was invented. A person is put inside a scanner, which is a large tube-shaped machine. Then he is X-rayed from all sides. A computer puts together all of these images and can show doctors more than a normal X-ray can. CTs are used for brain diseases and head injuries.

X-rays, however, can also do harm to your body. Patients must wear special protection for the parts of their body that are not X-rayed. Doctors and helpers who work with X-ray machines must wear lead aprons and stand behind screens.

X-rays are sometimes used to in the fight against cancer. Doctors often beam X-rays at cancer cells in order to destroy them.

CT scanner
Image: Tomáš Vendiš, CC BY-SA 4.0, via Wikimedia Commons

X-rays in science

Scientists often use X-rays to study the structure of other organisms or minerals that are in rock. By bombarding material with X-rays you can tell how old an object is.

Since the 1970s X-rays have been used to study stars and galaxies that are very far away. X-ray telescopes are put on board satellites that orbit far above the earth’s surface. They can see things that telescopes on earth cannot detect, because X-rays are absorbed by the earth’s atmosphere.

Chandra x-ray telescope, launched by NASA in 1999
Image: NASA/CXC/NGST, Public domain, via Wikimedia Commons

Other uses

Factories use X-rays to find cracks in machines or in metal objects. At airports X-ray machines scan millions of handbags and suitcases for weapons like bombs, guns or knives.

Luggage screening at an airport
Image:User:Mattesderivative work: Cherubino,
Public domain, via Wikimedia Commons

Exercises

Multiple Choice Test
Words and Definitions
Match the sentence parts
Missing Word Cloze
True or False ?
Crossword

Printable Downloads (PDF)

Word List
End of Unit Test
Key