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Science [1 Mark Questions]

Electricity · CBSE STD 10 (CBSE - English Medium). 103 questions.

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[1 Mark Questions]

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Question 11 Mark
Why should the resistance of:
A voltmeter be very large?
Answer
The resistance of a voltmeter should be very large so that it takes a negligible current from the current.
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Question 31 Mark
A resistance of 20 ohms has a current of 2 amperes flowing in it. What potential difference is there between its ends?
Answer
R = 20 ohms
I = 2 amp
We know that
V = IR
Thus,
V = 2 × 20
V = 40V
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Question 41 Mark
An electric bulb is rated at 220V, 100W. What is its resistance?
Answer
V = 220 V, P = 100W
R=?
We know that
$\text{P}=\frac{\text{V}_2}{\text{R}}$
Thus
$\text{R}=\frac{\text{V}_2}{\text{P}}=\frac{2202}{100}=484\ \text{ohm}$
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Question 51 Mark
An electric lamp is labelled 12V, 36W. This indicates that it should be used with a 12V supply. What other information does the label provide?
Answer
Other information is that it will consume energy at the rate of 36 J/s.
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Question 61 Mark
Write down an expression for the resistance of a metallic wire in terms of the resistivity.
Answer
$\text{R}=\rho\frac{\text{L}}{\text{A}}$
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Question 71 Mark
Name two effects produced by electric current.
Answer
Two effects of produced by electric current are:
  1. Heating effect.
  2. Magnectic effect.
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Question 81 Mark
Two resistances X and Y are connected turn by turn:
  1. In parallel, and
  2. In series. In which case the resultant resistance will be less than either of the individual resistances?
Answer
In case of parallel combination, the resultant resistance will be less than either of the individual resistances.
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Question 91 Mark
If the length of a wire is doubled by taking more of wire, what happens to its resistance?
Answer
Resistance also gets doubled.
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Question 101 Mark
Why are copper and aluminium wires usually used for electricity transmission?
Answer
Because copper and aluminium have very low resistivities.
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Question 111 Mark
What is nichrome? State its one use.
Answer
Nichrome is an alloy of nickel, chromium, manganese ad iron having a resistivity of about 60 times more than that of copper. It is used for making the heating elements of electrical heating appliances.
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Question 121 Mark
If the current passing through a conductor is doubled, what will be the change in heat produced?
Answer
Heat produced is directly proportional to the square of current.
If current I is doubled, heat H will be four times.
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Question 141 Mark
What is meant by saying that the electric potential at a point is 1 volt?
Answer
Electric potential at a point is 1 volt means 1 joule of work is done in moving 1 unit positive charge from infinity to that point.
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Question 151 Mark
How does the presence of impurities in a metal affect its resistance?
Answer
Presence of impurities in a metal increases the resistance.
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Question 161 Mark
State whether a voltmeter has a high resistance or a low resistance. Give reason for your answer.
Answer
Voltmeter has a high resistance so that it takes a negligible current from the circuit.
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Question 171 Mark
What property of the filament wire accounts for this difference?
Answer
High resistance of filament wire accounts for this difference.
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Question 201 Mark
How much work is done when one coulomb charge moves against a potential difference of 1 volt?
Answer
Potential difference = 1V
Electricity
Charge moved = 1C
Work done = Potential difference × Charge moved
= 1 × 1 = 1J
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Question 231 Mark
Name the unit of electrical resistance and give its symbol.
Answer
Unit of electrical resistance is ohm. its symbol is $\Omega$.
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Question 251 Mark
A current of 5 amperes flows through a wire whose ends are at a potential difference of 3 volts. Calculate the resistance of the wire.
Answer
I = 5 amp
p.d., V = 3V
We know that
V=IR
Thus,
3 = 5 × R
$\text{R}=\frac{3}{5}=0.6\ \text{ohm}$
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Question 261 Mark
What is the ratio of potential difference and current known as?
Answer
The ratio of potential difference and current is known as resistance.
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Question 271 Mark
The current passing through a room heater has been halved. What will happen to the heat produced by it?
Answer
The heat produced by the heater will become one-fourth because heat produced is directly proportional to the square of the current.
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Question 281 Mark
Which instrument is used to measure electric current? How should it be connected in a circuit?
Answer
An ammeter is used to measure electric current. It should be connected in series with the circuit.
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Question 311 Mark
What is the general name of the substances having infinitely high electrical resistance?
Answer
Insulators.
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Question 321 Mark
How does the heat H produced by a current passing through a fixed resistance wire depend onb the magnitude of current I?
Answer
Heat produced is directly proportional to the square of current.
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Question 361 Mark
Name the law which relates the current in a conductor to the potential difference across its ends.
Answer
Ohm’s law.
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Question 371 Mark
How does the wire in the filament of a light bulb behave differently to the other wires in the circuit when the current flows?
Answer
The filament wire becomes white hot where as other wires in the circuit do not get heated much.
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Question 381 Mark
Compare how an ammeter and a voltmeter are connected in a circuit.
Answer
Ammeter is connected in series in a circuit whereas voltmeter is connected in parallel.
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Question 421 Mark
A current of 4A flows around a circuit for 10s. How much charge flows past a point in the circuit in this time?
Answer
Given, I = 4amp, C, t = 10s
Q = ?
We know that:
$\text{I}=\frac{\text{Q}}{\text{T}}.$
Q = 4*10 = 40C.
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Question 431 Mark
Name two devices which work on the heating effect of electric current.
Answer
Electirc heater and electric fuse.
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Question 461 Mark
If the potential difference between the end of a wire of fixed resistance is doubled, by how much does the electric power increase?
Answer
$\text{P}=\frac{\text{V}_2}{\text{R}}$
R is fixed.
V becomes double.
Now, $\text{P}=\frac{(2\text{V})2}{\text{R}}=\frac{4\text{V}_2}{\text{R}}$
So, the electric power becomes four times its previous value.
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Question 471 Mark
What is meant by saying that the potential difference between two points is 1 volt?
Answer
The potential difference between two points is 1 volt means 1 joule of work is done in moving 1coulomb of electric charge from one point to the other.
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Question 491 Mark
Keeping the resistance constant, the potential difference applied across the ends of a component is halved. By how much does the current change?
Answer
V = R
Keeping R Constant, $\text{V}\propto\text{I}$
So, when V is halved, I also becomes half.
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Question 501 Mark
Why should the resistance of:
An ammeter be very small?
Answer
The resistance of an ammeter should be very small so that it may not change the value of the current flowing in the circuit.
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[1 Mark Questions] - Science STD 10 Questions - Vidyadip