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Answer the questions.[Phy-2M]

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Question 12 Marks
A battery of 9 V is connected in series with resistors of 0.2 Ω, 0.3 Ω, 0.4 Ω , 0.5 Ω and 12 Ω, respectively. How much current would flow through the 12 Ω resistor?
Answer
There is no current division occurring in a series circuit.

Current flow through the component is the same. given by Ohm's law as

V =  IR

I = V/R

Where,

R is the equivalent resistance of resistances $0.2\Omega , 0.3\Omega , 0.4\Omega , 0.5\Omega\text{ and }12\Omega.$ These are connected in series.

Hence, the sum of the resistances will give the value of R.

$\text{R}=0.2+0.3+ 0.4 + 0.5 + 12 = 13.4\Omega$

Potential difference, V = 9 V

$\text{I} = \frac{9}{13.4} = 0.671 \text{A}$

Therefore. the current that would flow through the $12\Omega$ resistor is 0.671 A.

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Question 22 Marks
The values of current I flowing in a given resistor for the corresponding values of potential difference V across the resistor are given below –
I (amperes)0.51.02.03.04.0
V (volts)1.63.46.710.213.2
Plot a graph between V and I and calculate the resistance of that resistor.
Answer
From the given data the I-V graph is a straight line as shown below:

Resistance of resistor $(\text{R})=\frac{\text{V}_\text{A}-\text{V}_\text{B}}{\text{I}_\text{A}-\text{I}_\text{B}}=\frac{12\text{V}-6\text{V}}{3.6\text{A}-1.8\text{A}}$

$= \frac{6\text{V}}{1.8 \text{A}} = 3.3\Omega$.

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Question 32 Marks
How is a voltmeter connected in the circuit to measure the potential difference between two points?
Answer
A voltmeter is connected in parallel across any two points in a circuit to measure the potential difference between them with its +ve terminal to the point at higher potential and -ve terminal to the point at lower potential of the source.
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Question 52 Marks
Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connected in parallel to electric mains supply. What current is drawn from the line if the supply voltage is 220 V?
Answer
Both the bulbs are connected in parallel. Therefore, potential difference across each of them will be 220 V, because no division of voltage occurs in a parallel circuit. Current drawn by the bulb of rating 100 W is given by, Power = Voltage × Current
Current = Power/Voltage = 60/220A
Hence, current drawn from the line = 100/220 + 60/220 = 0.727 A
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Question 62 Marks
Compare the power used in the 2 Ω resistor in each of the following circuits:
  1. A 6 V battery in series with 1 Ω and 2 Ω resistors.
  2. A 4 V battery in parallel with 12 Ω and 2 Ω resistors.
Answer
  1. $\text{I}=\frac{6}{1+2}=2 \ \text{A}$.

Since current flowing is same in both resistors, power used in $2\Omega$ resistor

(P1) = I2R = (2)2 × 2 = 8 W.

  1. Since both $12\Omega$ and $2\Omega$ are in parallel to the 4 V source, voltage across each resistor remain same.

$\therefore$ Power used in $2\Omega$ resistor

$(\text{P}_2)=\frac{\text{V}^2}{\text{R}}=\frac{{4}^2}{2}=\frac{16}{2}=8 \ \text{W}$

Comparing between the power used in both cases $=\frac{\text{P}_1}{\text{P}_2}=\frac{8\text{W}}{8\text{W}}=1$.

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Question 72 Marks
Show how you would connect three resistors, each of resistance 6 Ω, so that the combination has a resistance of (i) 9 Ω, (ii) 4 Ω.
Answer
  1. When two 6 $\Omega$ resistances are in parallel and the third is in combination to this, the equivalent resistance will be 9 $\Omega$.


  1. When two 6 $\Omega$ resistances are in series and the third is in parallel to them, then it will be 4 $\Omega$.

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Question 82 Marks
How many 176 Ω resistors (in parallel) are required to carry 5 A on a 220 V line?
Answer
Let a resistor of 176 Ω are joined in parallel. Then their combined resistance (R)

$\frac{1}{\text{R}}=\frac{1}{176}+\frac{1}{176}\dots\text{times}=\frac{\text{n}}{176} \ \text{or} \ \text{R}=\frac{176}{\text{n}} \ \Omega$

It is given that V = 220 V and I = 5 A

$\text{R}=\frac{\text{V}}{\text{I}} \ \text{or} \ \frac{176}{\text{n}}=\frac{220}{5} 44\ \Omega$

$\text{n}=\frac{176}{44}=4$, resistors should be joined in parallel.

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Question 92 Marks
A piece of wire of resistance $R$ is cut into three equal parts. These parts are then connected in parallel. If the equivalent resistance of this parallel combination is $R_1$, what is the value of the ratio $R_1: R$ ?
Answer
Resistance of each part is $\frac{R}{3} \Omega$ (as resistance is proportional to the length of the wire.)
$
\begin{aligned}
& \frac{1}{R_{ T }}=\frac{3}{R}+\frac{3}{R}+\frac{3}{R}=\frac{9}{R} \\
& \therefore R_1=\frac{R}{9} \therefore \frac{R_{ T }}{R}=\frac{1}{9}
\end{aligned}
$
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Question 102 Marks
Explain why, the current that makes the heater element very hot, only slightly warms the connecting wires leading to the heater.
Answer
The connecting wires of the heater get only slightly warm because they have extremely low resistance due to which negligible heat is produced in them by passing current.
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Question 112 Marks
Calculate the resistance of an electric bulb which allows a 10 A current when connected to a 220 V power source.
Answer
$R= \frac{V}{I}$

$R = \frac{\text{220 V}}{\text{10 A}}$

$\therefore R = \text{22 } \Omega$

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Question 122 Marks
A heating coil has a resistance of 200Ω. At what rate will heat be produced in it when a current of 2.5A flows through it?
Answer
Given: R = 200 ohms, I = 2.5amp, t = 1sec
We know that
H = I2RT
H = 2.52 × 200 × 1
H = 1250J/ s
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Question 132 Marks
What is an electric circuit? Distinguish between an open and a closed circuit.
Answer
  1. An electrical circuit is a closed path consisting of a power supply and one or more peripherals connected together by conductive wires. 
  2.  
  1. Closed: A closed circuit is one in which current can flow from negative end of the cell through the circuit back to the positive end of the cell.
  2. Open: An open circuit is one in which current cannot flow through the circuit as the circuit is 'open' or not completely connected.

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Question 142 Marks
A piece of wire of resistance $\text{20 } \Omega$ is drawn out so that its length is increased to twice its original length. Calculate the resistance of the wire in the new situation.
Answer
$\text{R}_{1} = \frac{\rho l}{\text{A}} = \text{20 } \Omega$

$\text{R}_{2} = \frac{2 \rho l}{\frac{1}{2}\text{A}}$

$= 4\frac{\rho l}{\text{A}} = 4 \text{R}_{1}$

$\therefore \text{R}_{2} = 4\times 20 = \text{80 }\Omega $

Alternate Answer

Resistance becomes 2 times due to increase in length.

Due to change in area it again becomes 2 times.

$\therefore$ New resistance becomes 4 times of the original resistance.

$\therefore \text{R = 4 }\times \text{20 }\Omega= \text{8 } \Omega$

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Question 152 Marks
The values of current (I) flowing through a given resistor of resistance (R), for the corresponding values of potential difference (V) across the resistor are as given below:

  
V (volts) 0.5 1.0 1.5 2.0 2.5 3.0 4.0 5.0
I (amperes) 0.1 0.2 0.3 0.4 0.5 0.6 0.8 1.0

Plot a graph between current (I) and potential difference (V) and determine the resistance (R) of the resistor.

Answer


From the graph,

Potential difference (V) = 5V

Current (I) = 1A

Resistance (R) $=\frac{\text{V}}{\text{I}}=5\Omega$

Thus, the resistance of given resistor is 5 ohms.

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Question 162 Marks
While studying the dependence of potential difference (V) across a resistor on the current (I) passing through it, in order to determine the resistance of the resistor, a student took 5 readings for different values of current and plotted a graph between V and I. He got a straight line graph passing through the origin. What does the straight line signify? Write the method of determining the resistance of the resister using this graph.
Answer

Straight line graph between potential difference (V) and current (I) shows that resistor is a linear element and follows Ohm's Law.

Calculation of Resistance:

At any point on the graph, resistance is given as,  $\text{R}=\frac{\text{V}_0(\text{value of potential difference at that point})}{\text{I}_0(\text{value of current at that point})}$

In other word, the slope of the graph at any point gives the value $\frac{1}{\text{R}}$

Hence,

Slope $=\frac{\text{I}_0}{\text{V}_0}=\frac{1}{\text{R}}$

$\Rightarrow\ \text{R}=\frac{1}{\text{slope}}=\frac{\text{V}_0(\text{value of potential difference at that point})}{\text{I}_0(\text{value of current at that point})}$

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Question 172 Marks
You are supplied with a number of $100 Ω$ How could you combine some of these resisters to make a $250 Ω$ resistor?
Answer
For obtaining 250 ohms, connect two 100 ohm in series with a parallel combination of two 100 ohms.
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Question 182 Marks
Write a low resistance device name which is always connected in series with the device through which the current is to be measured.
Answer
Instrument used to measure electric current is ammeter and Galvanometer both instrument has very low resistance in which Galvanometer has lowest resistance approx zero so it is the various device and the ideal device both instrument are connected in series so that current can be measured.
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Question 192 Marks
Will current flow more easily through a thick wire or a thin wire of the same material, when connected to the same source? Why?
Answer
The current will flow more easily through thick wire. It is because the resistance of a conductor is inversely proportional to its area of cross-section. If thicker the wire, less is resistance and hence more easily the current flows.
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Question 202 Marks
Why is a series arrangement not used for connecting domestic electrical appliances in a circuit?
Answer
A series arrangement is not used for connecting domestic electrical appliances in a circuit because if one electrical appliance stops working due to some defect, then all other appliance also stop working as the whole circuit is broken.
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Question 212 Marks
Why is an electric light bulb not filled with air? Explain why argon or nitrogen is filled in an electric bulb.
Answer
If air is filled in an electric bulb, then the extremely hot tungsten filament would burn up quickly in the oxygen of air. So, the electric bulb is filled with a chemically unreactive gas like argon or nitrogen. Thes gases do not react with the hot tungsten filament and hence prolong the life of the filament of the bulb.
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Question 222 Marks
Why does the cord of an electric heater not glow while the heating element does?
Answer
The cord of an electric heater is made up of metallic wire such as copper or aluminum which has low resistance while the heating element is made up of an alloy which has more resistance than its constituent metals. Also heat produced 'H' is
H = I2Rt
Thus, for the same current H oc R, so for more resistance, more heat is produced by heating element and it glows.
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Question 232 Marks
Why does the connecting cord of an electric heater not glow hot while the heating element does?
Answer
The connecting cord of the heater made of copper does not glow because negligible heat is produced in it by passing current (because of its extremely low resistance); but the heating element made of nichrome glows because it becomes red-hot due to the large amount of heat produced on passing current (because of its high resistance).
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Question 242 Marks
Why are the coils of electric irons and electric toasters made of an alloy rather than a pure metal?
Answer
Because,
  1. Resistivity of an alloy is much higher than that of a pure metal.
  2. An alloy does not undergo oxidation (or burn) easily even at high temperature.
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Question 252 Marks
Why are electric bulbs filled with chemically inactive nitrogen and argon?
Answer
The closed glass chamber of the bulb contains, an inactive (inert) gas, Argon. The glass chamber can't be filled with air as the presence of oxygen will cause the filament to burn, i.e. react with oxygen.An obviously, inert gas won't react with the filament. Nitrogen is also used like argon.
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Question 262 Marks
Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal?
Answer
The coils of electric toaster and electric iron are made of an alloy rather than a pure metal because of the following reasons;
  1. The resistivity of an alloy is higher than that of a pure metal.
  2. It has high melting point and does not oxidise.
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Question 272 Marks
Which uses more energy, a 250 W TV set in 1 hr, or a 1200 W toaster in 10 minutes?
Answer
Energy used by a TV set of power 250 W in 1 hour = P × t = 250 Wh.
Energy used by toaster of power 1200 W in 10 minute (10/60 h)
= P × t = 1200 W × 10/60 h = 200 Wh.
Therefore, TV set will use more energy.
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Question 282 Marks
Which of the following resistor arrangement, A or B, has the lower combined resistance?
Answer
Resistance of arrangement A is 10 ohm.

Combined resistance of arrangement B is caculated as follows:

$\frac{1}{\text{R}}=\frac{1}{10}+\frac{1}{1000}=\frac{(100+1)}{1000}$

$\text{R}=\frac{1000}{101}=9.9\ \text{ohm}$

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Question 292 Marks
Which of the following are conductors and which are insulators? Sulphur, Silver, Copper, Cotton, Aluminium, Air, Nichrome, Graphite, Paper, Porcelain, Mercury, Mica, Bakelite, Polythene, Manganin.
Answer
Conductor: Silver, Copper, Aluminum, Nichrome, Graphite, Mercury, Manganin.

Insulators: Sulphur, Cotton, Air, Paper, Porcelain, Mica, Bakelite, Polythene.

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Question 302 Marks
Which is the better way to connect lights and other electrical appliances in domestic wiring: series circuits or parallel circuits? Why?
Answer
Parallel circuits – Because if one electrical appliance stops working due to some defect, then all other appliances in the circuit will keep working properly.
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Question 312 Marks
Which has more resistance:
  1. A long piece of nichrome wire or a short one?
  2. A thick piece of nichrome wire or a thin piece?
Answer
  1. A long piece of nichrome wire.
  2. A thin piece of nichrome wire.
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Question 322 Marks
When a 12V battery is connected across an unknown resistor, there is a current of 2.5mA in the circuit. Calculate the value of the resistance of the resistor.
Answer
V = 12 volt, I = 2.5 × 10 - 3A

We know that

V = IR

$\text{R}=\frac{\text{V}}{\text{I}}$

$\text{R}=\frac{12}{(2.5\times10^{-3})}$

R = 4.8 × 103 ohm = 4800 ohm.

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Question 332 Marks
What p.d. is needed to send a current of 6A through an electrical appliance having a resistance of $40\Omega$?
Answer
I = 6 amp, R = 40 ohm
We know that
V=IR
V = 6 × 40 = 240V.
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Question 342 Marks
What kind of graph is obtained by plotting values of V and I Why?
Answer
T​he V - I graph (at constant temperature) for a conductor following the Ohm’s law is a straight line with a positive slope.

The slope of the graph with current on the vertical axis and potential difference on the horizontal axis represents the Resistance of the material of the conductor.
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Question 352 Marks
What is the potential difference between the terminals of a battery if 250 joules of work is required to transfer 20 coulombs of charge from one terminal of battery to the other?
Answer
Given: Work done = 250J, Charge moved = 20C.

we know that,Potential difference $= \frac{\text{Work done}}{\text{Charge\ moved}}$

$=\frac{250}{20}=12.5$

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Question 362 Marks
What is the maximum power in kilowatts of the appliance that can be connected safely to a 13A, 230V mains socket?
Answer
Potential Difference, V = 230V
Current, I = 13A
Power, P = V × I
= 230 × 13 = 2990W
= 2.99kW
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Question 372 Marks
What is the heating effect of electric current?
Answer
When an electric current is passed through a conductor, the conductor becomes hot after some time and produce heat. This happens due to the conversion of some electric energy passing through the conductor into heat energy. This phenomenon is known as the heating effect of electric current.
The heat (H) produced during the heating effect of electric current is given by the formula:
Heat, H = I2 Rt
Where, I = Current
R = Resistance of conductor
t = time
The SI unit of the heat produced is Joules (J).
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Question 382 Marks
What is the conventional direction of the flow of electric current? How does it differ from the direction of flow of electrons?
Answer
Conventional direction of flow of electric current is from positive terminal of a battery to the negative terminal, through the outer circuit. The direction of flow of electrons is opposite to the direction of conventional current, i.e. from negative terminal to positive terminal.
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Question 392 Marks
What is the commercial unit of electrical energy? Represent it in terms of joules.
Answer
The commercial unit of electrical energy is kilowatt hour.

1kWh = 11000Wh

1000Wh = (1000 Joule/ second) × hour

$=1000\times\frac{\text{J}}{\text{S}}\times60\times60\text{s}$

= 3600 × 1000J

= 3.6 × 106J

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Question 402 Marks
What is meant by the “resistance of a conductor”? Write the relation between resistance, potential difference and current.
Answer
The property of a conductor due to which it opposes the flow of current through it is called resistance of the conductor.

$\text{R}=\frac{\text{V}}{\text{I}}$

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Question 412 Marks
What is meant by the heating effect of current? Give two applications of the heating effect of current.
Answer

When an electric current is passed through a high resistance wire, the wire becomes very hot and produces heat. This effect is knows as heating effect of current. This effect is used in room heaters and electric ovens.

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Question 422 Marks
What is meant by saying that the potential difference between two points is 1 V?
Answer
If 1 J of work is required to move a charge of amount 1 C from one point to another, then it is said that the potential difference between the two points is 1 V.
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Question 432 Marks
What is meant by “electric power”? Write the formula for electric power in terms of potential difference and current.
Answer
The rate at which electrical work is done or the rate at which electrical energy is consumed is known as electrical power.
It is given by P = VI = Watt
P = VI = Watt
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Question 442 Marks
What is meant by conductors and insulators? Give two examples of conductors and two of insulators.
Answer
Conductors: Those substances through which electricity can flow are known as conductors.

E.g., Copper, silver etc.

Insulators: Those substances through which electricity cannot flow are known as insulators.

E.g., Plastic, cotton etc.

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Question 452 Marks
What is an electric current? What makes an electric current flow in a wire?
Answer
An electric currrent is a flow of electric charges (electrons) through a conductor. Potential difference between the ends of the wire makes electric current to flow in the wire.
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Question 462 Marks
What do you understand by the term “electric potential”? (or potential) at a point? What is the unit of electric potential?
Answer
The electric potential (or potential) at a point in an electric field is defined as the work done in moving a unit positive charge from infinity to that point.

Unit of electric potential is volt.

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Question 472 Marks
What do you understand by the “resistivity” of a substance?
Answer
Resistivity is the characteristic property of a substance which depends on the nature of the substance and its temperature. It is numerically equal to the resistance between the opposite faces of a 1m cube of the substance.
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Question 482 Marks
What do you understand by a mixed combination of resistances?
Answer
Mixed combination of resistance means when two or more than two resistors are connected in series and parralel simultaneously. Resistor circuits that combines series and parallel resistors networks together are generally known as resistor combination or mixed resistor circuits.
These type of combination are known as Mixed combination.

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Question 492 Marks
What does it mean a circuit is closed or open?
Answer
If a circuit is closed that means electrons can easily flow through the circuit and thus electric current will flow through it.
If a circuit is open that means the electrons will not be able to flow through the circuit which means that there will be no current flowing through it.
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Question 502 Marks
What current will be taken by a 920W appliance if the supply voltage is 230V?
Answer
P = 920W, V = 230V, I = ?
We know that
P = V × I,
920 = 230 x II = $\frac{920}{230}$ = 4amp
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Answer the questions.[Phy-2M] - Science STD 10 Questions - Vidyadip