Question Answers For All Chapters – General Science Class 8
Exercise
1. Write proper words from the following group of words in the blanks.
(magnetism, 4.5V, 3.0V, gravitational attraction, potential difference, potential, higher, lower, 0V)
a. Water in the waterfall flows from a higher level to the lower level because of gravitational attraction.
b. In an electric circuit, electrons flow from a point of higher potential to the point of lower potential.
c. The difference between the electrostatic potential of the positive end and the negative end of an electric cell is the potential difference of the cell.
d. Three electric cells of potential difference 1.5 V each have been connected as a battery. The potential difference of the battery will be 4.5V.
e. An electric current flowing in a wire creates magnetism around the wire.
2. A battery is to be formed by joining 3 dry cells them with connecting wires. Show how will you connect the wires by drawing a diagram.
Battery Connection Diagram:
- A battery is formed by connecting the positive terminal of one dry cell to the negative terminal of the next cell in a series. (You can draw a simple series circuit diagram showing three cells connected in a row.)
3. In an electric circuit, a battery and a bulb have been connected and the battery consists of two cells of equal potential difference. If the bulb is not glowing, then which tests will you perform in order to find out the reason for the bulb not glowing?
Tests to check why the bulb is not glowing:
- Check if the cells are properly connected.
- Ensure that the battery has sufficient charge.
- Inspect if the connecting wires are correctly attached.
- Check if the bulb filament is broken.
- Ensure the switch is in the “ON” position.
4. Electric cells having 2V potential difference each have been connected in the form of a battery. What will be the total potential difference of the battery in both cases?
Total potential difference of the battery:
- If two cells of 2V each are connected in series: 2V + 2V = 4V.
- If three cells of 2V each are connected in series: 2V + 2V + 2V = 6V.
5. Describe the construction, working and usefulness of a dry Cell, with the help of a diagram.
Dry Cell Construction and Working:
- Construction: A dry cell consists of a zinc container (negative terminal), a graphite rod (positive terminal), and an electrolyte of ammonium chloride and zinc chloride.
- Working: Due to a chemical reaction, electrons flow from the zinc case to the graphite rod, generating a potential difference and allowing electric current to flow in a circuit.
- Usefulness: Dry cells are compact, portable, and used in clocks, torches, and radios.
6. Describe the construction and working of an electric bell with the help of a diagram.
Electric Bell Construction and Working:
- Construction: An electric bell consists of an electromagnet, an iron strip with a striker, a contact screw, and a gong.
- Working: When the switch is pressed, current flows through the electromagnet, which pulls the iron strip. The striker hits the gong, making a sound. When the circuit breaks, the iron strip returns to its original position, and the process repeats.
- Usefulness: Electric bells are used in homes, schools, and industries for signaling.
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