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Science [1 Mark Questions]

electricity · Gujarat Board (GSEB) STD 10 (GSEB - English Medium). 73 questions.

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[1 Mark Questions]

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Question 11 Mark
Name the instrument used to measure ełectric current.
Answer
  • The electric current is measured by an instrument / device called Ammeter.
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Question 21 Mark
Name two characteristics of a heater coil.
Answer
  • A heater coil should have $(i)$ high resistivity and $(ii)$ high melting point.
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Question 31 Mark
Distinguish between the kilowatt and the kilowatt hour.
Answer
  • The kilowatt $(kW)$ is a unit of power and the kilowatt hour $(kWh)$ is a unit of electric energy.
  • $1 kWh = 1 kW \times 1h$
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Question 41 Mark
What causes the potential difference between the two terminals of a cell?
Answer
  • Chemical reactions taking place within a cell result in excess of electrons at the one terminal and deficiency of electrons at the other terminal.
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Question 51 Mark
How does the resistance of an ohmic conductor depend on the applied voltage?
Answer
  • Resistance R is a constant, so it does not depend upon the applied voltage.
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Question 61 Mark
A wire of resistivity ρ is pulled to double its length. What will be its new resistivity ?
Answer
  • Resistivity of wire remains the same as resistivity ρ depends on the nature of material and temperature.
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Question 71 Mark
How much energy is consumed by $2 \ kW \ AC$ when used for $2$ hour?
Answer
  • Electric energy $E = P \times t$
  • $= 2 kW \times 2$ hour
  • $= 4 kWh$
  • Where, 1 kWh $= 3.6 × 10^6$ J
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Question 81 Mark
Why is much less heat generated in long electric cables than in the filament of an electric bulb?
Answer
  • Electric cables are made of thick copper i.e.. their area of cross-section is large. Hence they have much less resistance as compared to the thin tungsten filament of an electric bulb.
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Question 91 Mark
The power-voltage rating of an electric appliance is $100 W -250 V$. What does it signify?
Answer
  • The electric appliance consumes a power of $100 W$ (i.e., an electric energy of $100J$ per second) when connected to a $250V$ electric supply.
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Question 101 Mark
$400 \ J$ of heat is produced in $4$ s in a $4 \Omega $ resistor. Find the potential difference across the resistor.
Answer
  • Here,$H=400 J$
  • $\therefore \frac{V^2 t}{R}=400$
  • $\therefore V ^2=400 \times \frac{R}{t}=400 \times \frac{4}{4}=400$
  • $\therefore V =20$ volts
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Question 121 Mark
Two wires have the same length, same radius but one of them is made of copper and the other is made of iron. Which will have more resistance?
Answer
  • As resistance $R =\rho \frac{l}{A}$ and resistivity $\rho $ for iron is more than that for copper, the iron wire will have more resistance.
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Question 131 Mark
How does the resistance of a metallic wire depend on its temperature?
Answer
  • The resistance of a metallic wire increases with temperature.
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Question 141 Mark
What can you say about the resistance of a voltmeter?
Answer
  • The resistance of a voltmeter should be very high, ideally infinite.
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Question 151 Mark
What can you say about the resistance of an ammeter?
Answer
  • The resistance of an ammeter should be very low, ideally zero.
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Question 161 Mark
If a number of bulbs of different wattages are joined in parallel with a voltage source, which bulb will glow with maximum brightness?
Answer
  • The bulb with highest wattage (here, lowest resistance) will glow with maximum brightness$P =\frac{V^2}{R}$ as and here $P \propto \frac{1}{R}$
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Question 171 Mark
How is heat produced in a conductor by an electric current?
Answer
  • Heat produced in a conductor by an electric current is due to collisions of free electrons with the ions and atoms in the conductor.
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Question 181 Mark
What is the difference between a resistor and resistance?
Answer
  • A resistor is a component whereas resistance is its property due to which it opposes the flow of electrons through it.
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Question 191 Mark
Why is lead-tin alloy used for making a fuse?
Answer
  • Lead-tin alloy has low melting point. Hence it is used for making a fuse.
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Question 201 Mark
A electric lamp is labelled $12 V, 36 W$. This indicate that it should be used with a $12 V$ supply. What other information does the label provide?
Answer
  • The electric lamp consumes electric energy at the rate of $36 J/s.$
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Question 211 Mark
A potential difference of $10 \ V$ is needed to make a current of $0.02 \ A$ flow through a wire. What potential difference is needed to make a current of $250$ mA to flow through the same wire?
Answer
  • According to the Ohm's law,
  • $R =\frac{v}{l}$ 
  • So, $R =\frac{10}{0.02}$ 
  • $= 500 \Omega $
  • Now, to make a current of
  • $250 \ mA = 250 \times 10^-3$ A to flow through the same wire, the required potential difference is
  • $V = IR = 250 \times 10^-3 \times 500 = 125 \ V$
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Question 221 Mark
Keeping the potential difference constant, the resistance of a circuit is halved. How does the current change?
Answer
  • The current becomes double the initial current.
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Question 231 Mark
Keeping the resistance constant, the potential difference applied across the ends of a component is halved. How does the current change?
Answer
  • The current becomes half the initial current.
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Question 241 Mark
Which of the following statements is correct? A. one volt is one joule per ampere. B. one volt is one joule per coulomb.
Answer
  • B. one volt is one joule per coulomb.
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Question 251 Mark
Four students connect $4$ cells of $1.5 \ V$ each to get a battery of voltage $6 \ V$. State the incorrect connection/ connections. Justify your answer.
Answer
  • $A, B$ and $C$ are incorrect connections ($D$ is correct).
  • Because for a proper series connection of four cells, each of $1.5 \ V$ to obtain a battery of $6 \ V$, the negative terminal of each cell should be connected to the positive terminal of the next cell or the positive terminal of each cell should be connected to the negative terminal of the next cell (connection $D$).
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Question 261 Mark
What determines the rate at which energy is delivered by a current?
Answer
  • The electric power of the source determines the rate at which energy is delivered by the current to the load / appliance.
  • [Whereas the electric power of an appliance determines the rate at which energy delivered by a current is consumed by appliance.]
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Question 271 Mark
Name a device that helps to maintain a potential difference across a conductor.
Answer
  • An electric cell or battery is a device that helps to maintain a potential difference across a conductor.
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Question 281 Mark
Name the instrument used to measure electric potential difference.
Answer
  • The electric potential difference is measured with the instrument / device called voltmeter.
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Question 291 Mark
Name the physical quantity responsible for a flow of electrons in a metal wire.
Answer
  • Potential difference (i.e., difference of electric pressure) across a metal wire is responsible for a flow of electrons in a metal wire.
  • [This difference of potential may be produced by a cell or a battery consisting of two or more cells.]
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Question 301 Mark
What is an electric circuit?
Answer
  • An electric circuit is a continuous and closed path of an electric current.
OR
  • A continuous and closed path consisting of conducting wires and other electrical components along which an electric current flows is called an electric circuit.
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Question 311 Mark
What is a switch?
Answer
  • A switch is a component that can provide a conducting link between the cell (or battery) and other electrical components of electric circuit.
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Question 321 Mark
To verify the Ohm's law a circuit diagram was drawn by a student as shown below :
Answer
  • $K =$ voltmeter, $L =$ rheostat, $M =$ ammeter and $N =$ plug key
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Question 331 Mark
Find the minimum resistance that can be made using five resistors, each of $5 \Omega$.
Answer
  • By connecting given resistors in parallel, resistance $1 \Omega $ is obtained which is the minimum.
  • $R _{ p }=\frac{R}{n}=\frac{5 \Omega}{5}=1 \Omega$
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Question 341 Mark
Which of the following bulbs has more resistance? $A. A 220 \ V, 100 \ W$ bulb $B. a 220 \ V, 60 \ W$ bulb.
Answer
  • $60 \ W$ bulb
  • Here $R \propto \frac{1}{p}(\because$ as both the bulbs have the same voltage rating.)
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Question 371 Mark
Name a substance whose resistance almost remains unchanged with a change in temperature.
Answer
  • Manganin (an alloy of $Cu, Mn$ and $Ni)$
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Question 381 Mark
Which bulb will glow with maximum brightness in case bulbs of different wattages are joined in series with a voltage source?
Answer
  • The bulb with highest wattage (here highest resistance) will glow with maximum brightness as $P =I^2 R$ and here $P \alpha R.$
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Question 391 Mark
How does the potential difference divide itself in a series combination of resistors?
Answer
  • In a series combination of resistors, the potential difference across any of the resistors is directly proportional to its resistance.
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Question 401 Mark
How does the current divide itself in a parallel combination of resistors?
Answer
  • In a parallel combination of resistors, the current divides in the inverse ratio of the resistances.
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Question 411 Mark
What do you mean by the term load in an electric circuit?
Answer
  • Electric lamps, heaters, air conditioners, motors and other devices which work on electricity are called loads because they consume electric energy.
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Question 421 Mark
The voltage-current $(V-l)$ graphs for a metallic conductor at two different temperatures $T_1$ and $T_2$ are shown below:
Answer
  • At temperature $T_1$.
  • Because the slope $\left(\frac{\Delta V}{\Delta I}\right)$of the graph i.e., its resistance is greater at $T_1.$
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Question 431 Mark
How is a voltmeter connected in the circuit to measure the potential difference between two points?
Answer
  • A voltmeter is (always) connected in parallel across the points in the circuit between which the potential difference is to be measured.
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Question 441 Mark
Why are Constantan and Manganin used for making standard resistors?
Answer
  • The resistivity of Constantan and Manganin is moderate and almost independent of temperature.
  • Hence, these materials are used for making standard resistors.
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Question 451 Mark
Why is Nichrome used as a heating element?
Answer
  • Nichrome (alloy) has high resistivity and high melting point. Moreover, it does not react with air when it is red-hot $(800 ^\circ C).$
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Question 461 Mark
Under what conditions is the Ohm's law applicable?
Answer
  • The Ohm's law is applicable when the physical conditions like temperature, pressure, etc. of a conductor do not change when a potential difference is applied across it.
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Question 471 Mark
Why are the filament-type electric light bulbs not power efficient?
Answer
  • When electric power is supplied to the filament-type electric light bulb, most of the electric power consumed by the filament appears as heat (due to which the bulb becomes hot), only a small amount of electric power is converted into light. So, the filament-type electric light bulbs are not power efficient.
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Question 491 Mark
Name two devices whose working is based on the heating effect of electric current.
Answer
  • An electric iron, electric toaster
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Question 501 Mark
Name and define the smallest commercial unit of electricity.
Answer
  • The smallest commercial unit of electricity is the watt-hour $(Wh).$
  • It is defined as the amount of electric energy consumed by an electrical device of power rating 1W in one hour.
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