#### Chapters

Chapter 2: Work and Energy

Chapter 3: Current Electricity

Chapter 4: Measurement of Matter

Chapter 5: Acids, Bases and Salts

Chapter 6: Classification of Plants

Chapter 7: Energy Flow in an Ecosystem

Chapter 8: Useful and Harmful Microbes

Chapter 9: Environmental Management

Chapter 10: Information Communication Technology (ICT)

Chapter 11: Reflection of Light

Chapter 12: Study of Sound

Chapter 13: Carbon : An important element

Chapter 14: Substances in Common Use

Chapter 15: Life Processes in Living Organisms

Chapter 16: Heredity and Variation

Chapter 17: Introduction to Biotechnology

Chapter 18: Observing Space : Telescopes

## Chapter 3: Current Electricity

#### Balbharati solutions for Maharashtra state board Class 9 Science and Technology Chapter 3 Current Electricity Exercise [Pages 44 - 45]

The accompanying figure shows some electrical appliances connected in a circuit in a house. Answer the following questions.

The following figure shows the symbols for components used in the accompanying electrical circuit. Place them at proper places and complete the circuit.

Which law can you prove with the help of above circuit ?

Umesh has two bulbs having resistances of 15 W and 30 W. He wants to connect them in a circuit, but if he connects them one at a time the filament gets burnt. Answer the following.

A.Which method should he use to connect the bulbs?

B. What are the characteristics of this way of connecting the bulbs depending on the answer of A above

C . What will be the effective resistance in the above circuit?

The following table shows current in Amperes and potential difference in Volts.

Find the average resistance.

The following table shows current in Amperes and potential difference in Volts.

What will be the nature of the graph between the current and potential difference? (Do not draw a graph.)

The following table shows current in Amperes and potential difference in Volts.

Which law will the graph prove? Explain the law.

Match the pairs

‘A’ Group |
‘B’ Group |

1.Free electrons | a. V/ R |

2. Current | b. Increases the resistance in the circuit |

3. Resistivity | c. Weakly attached |

4. Resistances in series | d. VA/LI |

The resistance of a conductor of length x is r. If its area of crosssection is a, what is its resistivity? What is its unit?

Resistances R_{1,} R_{2}, R_{3} and R_{4} are connected as shown in the figure. S1 and S2 are two keys. Discuss the current flowing in the circuit in the following cases.

a. Both S_{1} and S_{2} are closed.

b. Both S_{1} and S_{2} are open.

c. S_{1} is closed but S_{2} is open.

Three resistances x1, x2 and x3 are connected in a circuit in different ways. x is the effective resistance. The properties observed for these different ways of connecting x1, x2 and x3 are given below. Write the way in which they are connected in each case. (I-current, V-potential difference, x-effective resistance)

a. Current I flows through x1, x2 and x3

b. x is larger than x1, x2 and x3

c. x is smaller than x1, x2 and x3

d. The potential difference across x1, x2 and x3 is the same

e. x = x1 + x2 + x3

f. x = `1/(1/X_1 + 1/X_2 + 1/X_3)`

Solve the following problem.

The resistance of a 1m long nichrome wire is 6 W. If we reduce the length of the wire to 70 cm. what will its resistance be? (Answer : 4.2 W)

Solve the following problem.

When two resistors are connected in series, their effective resistance is 80 W. When they are connected in parallel, their effective resistance is 20 W. What are the values of the two resistances? (Answer : 40 W , 40 W)

Solve the following problem.

If a charge of 420 C flows through a conducting wire in 5 minutes what is the value of the current? (Answer : 1.4 A)

## Chapter 3: Current Electricity

## Balbharati solutions for Maharashtra state board Class 9 Science and Technology chapter 3 - Current Electricity

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Concepts covered in Maharashtra state board Class 9 Science and Technology chapter 3 Current Electricity are Potential Difference, Free Electrons, Electric Current, Resistance and Ohm'S Law, Electric Circuit, Conductors and Insulators, Experimental Proof of Ohm'S Law, System of Resistors and Effective Resistance.

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