Unit-8

2. Differentiate between:

a.

Current Electricity	Static Electricity
Flow of electric charges through a conductor.	Accumulation of electric charges on an object.
Caused by a potential difference in a circuit.	Caused by friction, conduction, or induction.
Continuous movement of electrons.	Charges remain stationary until discharged.

b.

Series Combination	Parallel Combination
Components are connected end to end.	Components are connected in separate branches.
Same current flows through all components.	Current is divided among branches.
Total voltage is the sum of individual voltages.	Voltage remains the same across all branches.
If one component fails, the circuit breaks.	If one component fails, others still work.

3. Give reason:

a. It is dangerous to stay under a tall tree or building while it is lightning.

• Lightning is an electrical discharge that tends to strike tall objects like trees or buildings. If a person is under a tall tree, they may get electrocuted due to the conduction of electricity.

b. Pieces of paper get attracted to a comb after combing hair with it.

• When a comb is rubbed against hair, it gains static charge due to friction. The charged comb then attracts small pieces of paper due to electrostatic force.

c. Crackling sound is heard while taking off woolen clothes at dark.

• When woolen clothes are removed, friction occurs, which creates static electricity. This causes tiny electric discharges, producing a crackling sound.

4. Answer the following questions:

a. What is electrostatic force? How is it produced? Describe.

• Electrostatic force is the force exerted by a charged object on another charged or neutral object. It is produced when an object gains or loses electrons due to friction, conduction, or induction.

b. What is static electricity? Write any three effects of it.

• Static electricity is the buildup of electric charges on the surface of an object.
  Effects:
  1. It causes materials to attract or repel each other.
  2. It produces sparks, such as during lightning.
  3. It can damage sensitive electronic devices.

c. What is lightning? How is it produced? Explain.

• Lightning is a sudden discharge of static electricity in the atmosphere. It is produced when clouds rub against each other, creating a difference in electric charge. When the charge difference becomes too high, electrons jump from one cloud to another or to the ground, creating lightning.

d. How can we save a house or building from lightning?

• By installing a lightning rod on top of buildings. It safely conducts the electric charge into the ground, preventing damage.

e. What is the combination of cells? Why is it done?

• The combination of cells refers to connecting two or more cells to increase voltage or current. It is done to provide the required electrical energy to operate devices.

f. Which combination of cells is used to increase the brightness of a bulb? Describe with a diagram.

• Series combination is used to increase the brightness of a bulb because the total voltage of the cells adds up, increasing the potential difference across the bulb.

g. Draw diagrams to show series combination and parallel combination of two cells separately.

h. You have a torchlight that needs 3V electricity. How will you connect the cells using two cells each of 1.5V? What are the advantages of such a combination?

• The two 1.5V cells should be connected in series to get 3V (1.5V + 1.5V = 3V).
  Advantages:
  1. Provides higher voltage to run the torch.
  2. Ensures consistent brightness.

i. You have a radio that needs 3V electricity. How will you hear the radio using two cells? Draw the diagram for such a combination of cells.

• The two 1.5V cells should be connected in series to obtain the required 3V.
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j. Study the given figure and answer the questions: 

i. What type of combination of cell does it have?

• It shows a series combination of cells.

ii. What happens in brightness of the bulb when the number of cells is increased? Give reason.

• The brightness of the bulb increases because more cells in series increase the total voltage supplied to the bulb.

iii. Write the uses of such a combination.

• Used in torches, emergency lights, and electrical circuits requiring higher voltage.

k. Study the picture and answer the following questions: 

i. What is shown in the picture?

• A lightning rod installed on a building.

ii. For what purpose is it used?

• It is used to protect buildings from lightning strikes by safely directing the electric charge into the ground.

iii. How does lightning occur when a negatively charged cloud comes just above a house? Explain with a diagram.

• When a negatively charged cloud moves above a building, it induces a positive charge on the ground. Once the charge difference is large enough, electrons jump from the cloud to the ground, creating a lightning strike. The lightning rod provides a safe path for the charge to flow into the ground.