Answer the following question.

Question 13 Marks

Three resistances 15Ω, 20Ω and 10Ω are connected in parallel. Find the effective resistance of the circuit.

Answer

Maharashtra Board Class 9 Science Solutions Chapter 3 Current Electricity 10

Maharashtra Board Class 9 Science Solutions Chapter 3 Current Electricity 11

The effective resistance of the circuit is 4.615 Ω. It is less than the least of the three i.e., 10Ω.

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Question 23 Marks

If three resistors $15Ω, 3Ω$ and $4Ω$ each are connected in series, what is the effective resistance in the circuit?

Answer

Given:
$R_1 =15Ω$
$R_2 = 3Ω$
$R_3 = 4Ω$
Effective resistance in series $(R_s) = ?$
$R_s = R_1 + R_2 + R_3$
$R_s = 15 + 3 + 4$
$R_s = 22Ω$
The effective resistance in the circuit is $22Ω$.

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Question 33 Marks

A current of 0.24 A flows through a conductor when a potential difference of 24 V is applied between its two ends. What is its resistance?

Answer

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Question 43 Marks

The length of a conducting wire is 50 cm and its radius is 0.5 mm. If its resistance is 30Ω, what is the resistivity of its material?

Answer

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Question 53 Marks

The resistance of the filament of a bulb is 1000Ω. It is drawing a current from a source of 230 V. How much current is flowing through it?

Answer

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The current flowing through the filament of bulb is 0.23 A.

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Question 63 Marks

Find the amount of work done if 3 C of charge is moved through a potential difference of 9 V.

Answer

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The work done is 27 joule.

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Question 73 Marks

A current of 0.4 A flows through a conductor for 5 minutes. How much charge would have passed through the conductor?

Answer

Given: Current (I) = 0.4 A
Time (t) = 5 min = 5 x 60 = 300 s
To find: Charge (Q) =?
Formula: Q = 1 x
Solution: Q = 0.4 x 300
Q= 120 C.
Charge passing through the conductor is 120

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Question 83 Marks

explain the statement : Bulbs arranged in parallel glow brighter than bulbs arranged in series.

Answer

The amount of light given out by bulbs in parallel combination will be more than that in series combination.
In parallel combination the resistance of the overall circuit decreases whereas in series it increases, so the current flowing through the bulbs in parallel circuit is more.
Due to this, intensity of light given out by bulbs in parallel combination is more than the bulbs in series combination.

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Question 93 Marks

explain the statement : Fuse used in electrical circuit can save electrical objects from damage.

Answer

Fuse wire is used to protect domestic appliances.
It is made of a mixture of substances and has a specific melting point.
It is connected in series to the electric appliances. If for some reason, the current in the circuit increases excessively, the fuse wire gets heated and melts.
The circuit gets broken and the flow of current stops, thus protecting the appliance.
This wire is fitted in a groove in a body of porcelain-like non-conducting material. For domestic use, fuse wires with upper limits of 1 A, 2 A, 3 A, 4 A, 5 A and 10 A are used.

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Question 103 Marks

explain the statement : In a domestic circuit colour code is followed while setting up electrical wiring.

Answer

The electricity in our homes is brought through the main conducting cable either from the electric pole or from underground cables.
Usually, there are three wires in the cable.
(a) Live wire which brings in the current. It has a red or brown insulation.
(b) Neutral wire through which the current returns. It is blue or black.
(c) Earth wire is of yellow or green colour. This is connected to a metal plate buried deep underground near the house and is for safety purposes.
In India, the voltage difference between the live and neutral wires is about 220 V.
Live and neutral wires are connected to the electric meter through a fuse.
They are connected through a main switch, to all the conducting wires inside the home so as to provide electricity to every room.
In each separate circuit, various electrical appliances are connected between the live and neutral wires.
The different appliances are connected in parallel and the potential difference across every appliance is the same.

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Question 113 Marks

explain the statement : Safety precautions are to be taken while using electricity.

Answer

Electric switches and sockets should be fitted at a height at which small children cannot reach and put pins or nails inside. Plug wires should not be pulled while removing a plug from its socket.
Before cleaning an electrical appliance it should be switched off and its plug removed from the socket.
One’s hands should be dry while handling an electrical appliance, and, as far as possible, one should use footwear with rubber soles.
As rubber is an insulator, it prevents the current from flowing’ through our body, thereby protecting it.
If a person gets an electric shock, you should not touch that person. You should switch off the main switch or remove the plug from the socket if possible.
If not, then you should use a wooden pole to push the person away from the electric wire.

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