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CBSE Sample Paper Class 8 Science Chemical Effects Of Electric Current
1.) Answer the short questions (10×1)
a.) Which materials are called good conductors of electricity?
b.) Which materials are called poor conductors of electricity?
c.) What are electrodes?
d.) What is electroplating?
e.) A weak current can light which type of bulb?
f.) Give an example of electroplating in our daily life.
g.) Which type of liquids are commonly good conductors of electricity?
h.) Which process is used for the purification of metal?
i.) Why every type of liquid doesn’t conduct electricity?
j.) Which are the positive and negative electrodes?
2.) Briefly answer the following questions (3×3)
a.) How a bulb glows?
b.) Does pure water conducts electricity? If not how can we make it conduct electricity?
c.) Electric current can produce how many types of effect and what are those?
3.) Fill in the blanks (9×1)
a.) If electrodes are immersed in water and current is passed ______ and _______ bubbles are produced.(2 marks)
b.) A layer of any desired metal on another metal is done by _______ process.
c.) Liquid needs _______ for the conduction of electricity.
d.) Electroplating is used for _______ of metals.
e.) In copper sulphate purification process, the copper gets deposited in _______ electrode.
f.) Negative charged ions are called _______ .
g.) Pure water doesn’t contain ______ .
h.) Anode is a ______ electrode.
4.) Write true or false (7×1)
a.) Distilled water is a good conductor of electricity.
b.) Electricity can pass through liquid.
c.) Electroplating is used for purification of metal.
d.) LED bulbs can glow with weak electricity.
e.) Ions aren’t needed in liquid to conduct electricity.
f.) Electric current can produce only chemical effect.
g.) Plastic can be used as electrode.
5.) Fill the column with appropriate answer (10×1)
| Name | Good conductor | Poor conductor |
| Salt water | ||
| Lime juice | ||
| Honey | ||
| Milk | ||
| Vinegar | ||
| Sugar solution | ||
| Caustic soda solution | ||
| Coconut oil | ||
| Soda water | ||
| Rainwater |
6.) Name some of the items in your area that are electroplated. (5×1)
Answer
1.) Answer the short questions (10×1)
a.) Which materials are called good conductors of electricity?
Answer – Materials such as metals, liquids can conduct electricity through them so they are called good conductors of electricity.
b.) Which materials are called poor conductors of electricity?
Answer –Materials such as plastic, rubber etc. can’t conduct electricity through them so they are called poor conductors of electricity.
c.) What are electrodes?
Answer –Electrodes are electric conductors. They are used to carry electric to non-electric materials, such as solids, liquids etc.
d.) What is electroplating?
Answer – Electroplating is a process in which layer of one metal is deposited on another metal by using electricity.
e.) A weak current can light which type of bulb?
Answer – A weak current can light LED bulbs.
f.) Give an example of electroplating in our daily life.
Answer –An example of electroplating in our daily life is kitchenware.
g.) Which type of liquids are commonly good conductors of electricity?
Answer – Most of the liquids such as solutions of acids, bases and salts are commonly good conductors of electricity.
h.) Which process is used for the purification of metal?
Answer – Electroplating is the process used for purification of metal.
i.) Why every type of liquid doesn’t conduct electricity?
Answer – Every type of liquid doesn’t conduct electricity because it should contain ions in order to conduct electricity.
j.) Which are the positive and negative electrodes?
Answer – Positive electrode is Anode and negative electrode is Cathode.
2.) Briefly answer the following questions (3×3)
a.) How a bulb glows?
Answer –Bulb glows when electric current is passed through it. Electric current has a heating effect. When the electric current is passed through the bulb, the filament of the bulb gets heated. When the filament is heated it starts to glow. This is how a bulb glows.
However, weak electric current can’t heat the filament properly so it might glow.
b.) Does pure water conducts electricity? If not how can we make it conduct electricity?
Answer – Pure water or distilled water doesn’t conducts electricity.
We can change this by dissolving some salt into the distilled water. This happens because solution of salts are good conductors of electricity. So after dissolving the distilled water becomes salt solution.
c.) Electric current can produce how many types of effect and what are those?
Answer – Electric current produces three types of effect.
These effects are,
- Chemical effect
- Magnetic effect
- Heating effect
3.) Fill in the blanks (9×1)
a.) If electrodes are immersed in water and current is passed hydrogen and oxygen bubbles are produced. (2 marks)
b.) A layer of any desired metal on another metal is done by electroplating
c.) Liquid needs ions for the conduction of electricity.
d.) Electroplating is used for purification of metals.
e.) In copper sulphate purification process, the copper gets deposited in negative
f.) Negative charged ions are called anions .
g.) Pure water doesn’t contain ions .
h.) Anode is a positive
4.) Write true or false (7×1)
a.) Distilled water is a good conductor of electricity.
Answer –False
b.) Electricity can pass through liquid.
Answer – True
c.) Electroplating is used for purification of metal.
Answer – True
d.) LED bulbs can glow with weak electricity.
Answer – True
e.) Ions aren’t needed in liquid to conduct electricity.
Answer – False
f.) Electric current can produce only chemical effect.
Answer –False
g.) Plastic can be used as electrode.
Answer – False
5.) Fill the column with appropriate answer (10×1)
| Name | Good conductor | Poor conductor |
| Salt water | ✅ | |
| Lime juice | ✅ | |
| Honey | ✅ | |
| Milk | ✅ | |
| Vinegar | ✅ | |
| Sugar solution | ✅ | |
| Caustic soda solution | ✅ | |
| Coconut oil | ✅ | |
| Soda water | ✅ | |
| Rainwater | ✅ |
6.) Name some of the items in your area that are electroplated. (5×1)
Answer –
Some electroplated items are,
- Kitchenware
- Mobile
- Coins
- Jewellery
- Different machinery parts
