Electricity Class 10 Worksheet Science Chapter 11

Objective Type Questions

Q1: Two resistors of resistances 2 Ω and 4 Ω when connected to a battery will have
(a) Same current flowing through them when connected in parallel
(b) Same current flowing through them when connected in series
(c) Same potential difference across them when connected in series
(d) None of these
Ans: B
When two resistors are connected in series, the same current flows through both of them, irrespective of their resistances. As per Ohm’s law, the current (I) flowing through a circuit is directly proportional to the voltage (V) and inversely proportional to the resistance (R). So, if the resistors are in series, the total resistance is the sum of the individual resistances, but the current remains the same.

Q2: The resistance of an electric iron drawing a current of 4A when connected to a 220V mains would be
a) 1000 Ω
b) 55 Ω
c) 44 Ω
d) 64 Ω
Ans: B
The resistance (R) of an electric appliance can be calculated using Ohm’s law, which states that R = V/I, where V is the voltage and I is the current. Given that the iron is connected to a 220V mains and draws a current of 4A, the resistance would be 220/4 = 55 Ω.

Q3: If 25 joule of work is done in moving a charge of 5C across two points A and B the potential difference between these points would be
a) V
b) 125V
c) 5V
d) 625V
Ans: C

The potential difference (V) between two points in an electric circuit is defined as the work done (W) in moving a unit positive charge from one point to another. It is given by the equation V = W/Q, where Q is the charge. Hence, if 25 joules of work is done in moving a charge of 5C, the potential difference would be 25/5 = 5V.

Q4: Ohm’s law states the relationship between
a) Electric current and heat produced in it
b) Electric power and work done
c) Electric current and potential difference
d) Electric current and electric charge
Ans: C

Ohm's law states that the electric current flowing through a conductor is directly proportional to the potential difference across its ends, provided the physical conditions and temperature remain constant. This law forms the basis of many electrical and electronic principles and applications.

Q5: If electrons flow from A to B, current will flow from
(a) A to B
(b) B to A
(c) It will not flow
(d) None of these
Ans: B
The flow of electric current is considered to be the opposite to the direction of the flow of electrons. This is because the electrons carry a negative charge, and current is defined as the flow of positive charge. Hence, if electrons flow from A to B, the current is said to flow from B to A.

Q6: Unit of electric power may also be expressed as
a) Volt ampere
b) Kilowatt hour
c) Watt second
d) Joule second
Ans: A
Electric power is the rate at which electrical energy is transferred in an electrical circuit. It is usually measured in watts (W). One watt is equal to one volt-ampere, which is the product of electric potential difference (in volts) and electric current (in amperes).

Q7: Electric current flows from ‘A’ to ‘B’ in metallic conductor. The point is at higher potential is
(a) A
(b) B
(c) Both have equal potential
(d) Both have lower potential
Ans: A
Electric current always flows from a point of higher potential to a point of lower potential in a metallic conductor. Hence, if the current is flowing from 'A' to 'B', then 'A' is at a higher potential than 'B'.

Q8: When a 4V battery is connected across an unknown resistor there is a current of 100 mA in the circuit.
The value of the resistance of the resister is:
(a) 4 Ω
(b) 40 Ω
(c) 400 Ω
(d) 0.4 Ω
Ans: B
The resistance of a resistor can be calculated using Ohm’s law, which states that R = V/I (Resistance = Voltage/Current). Given that the voltage across the resistor is 4V and the current is 100 mA (0.1 A), the resistance would be 4/0.1 = 40 Ω.

Q9: In an electric circuit three incandescent bulbs of rating 40W, 60W and 100W respectively are connected in parallel to an electric source. Which of the following is likely to happen regarding their brightness
a) Brightness of all the bulbs will be the same
b) Brightness of bulb A will be the maximum
c) Brightness of bulb B will be more than that of A
d) Brightness of bulb C will be less than that of B
Ans: C
The brightness of an incandescent bulb is directly proportional to its power rating. When bulbs of different power ratings are connected in parallel to an electrical source, the bulb with the higher power rating will be brighter. Hence, the 60W bulb will be brighter than the 40W bulb.

Q10: Electrical resistivity of a given metallic wire depends upon
(a) its length
(b) its thickness
(c) its shape
(d) nature of the material
Ans: D
Electrical resistivity is a property that depends on the material of the wire, not its length, thickness, or shape. Different materials have different abilities to resist the flow of electric current, which is why the nature of the material determines the wire's resistivity.

Fill in the Blanks

Q1: The SI unit of electric potential difference is ___________.
Ans: Volt
The SI unit of electric potential difference is Volt (V).

Q2: George Simon Ohm established the relationship between current (I) and potential difference (V) using the formula V = __________.
Ans: IR
Ohm's law is represented by the equation V = IR.

Q3: The heating effect of electric current is utilized in devices like electric iron, electric toasters, and electric __________.
Ans: Heaters
The heating effect is also used in electric ovens, electric kettles, etc.

Q4: In a parallel arrangement of resistances, the total current is the sum of the currents flowing through different resistances, and the sum of the reciprocals of the separate resistances is equal to the reciprocal of the equivalent resistance, given by __________.
Ans: 1/Rp
The formula for equivalent resistance in parallel arrangement is given by 1/Rp = 1/R1 + 1/R2 + 1/R3 + ...

Q5: The practical unit of electric energy is a ____________, where 1 kW h = 3.6 x 10⁶ J.
Ans: Kilowatt-hour
Kilowatt-hour (kW h) is a practical unit of electric energy.

Match the Column (In a Table):

Q1:

Ans: 

Assertion and Reasoning Questions

Q1: The following questions consists of two statements –Assertion(A) and Reason (R). Answer these questions selecting the appropriate option given below.
Assertion (A): If a graph is plotted between potential difference and current the graph is a straight line passing through the origin.
Reason(R): current is directly proportional to the potential difference.
a) Both A and R are true and R is the correct explanation for A
b) Both A and R are true and R is not the correct explanation for A
c) A is true but R is false
d) A is false but R is true.
Ans: A
The assertion and reason are both correct and related in this case. According to Ohm's law, the current flowing through a conductor is directly proportional to the potential difference across its ends, given that the temperature remains constant. This relationship is linear, so when graphed with current on the y-axis and potential difference on the x-axis, the result is a straight line that passes through the origin.

Q2: The following questions consists of two statements –Assertion(A) and Reason (R). Answer these questions selecting the appropriate option given below.
Assertion (A): Longer wires have greater resistance and the smaller wires have lesser resistance.
Reason(R): Resistance is inversely proportional to the length of the wire.
a) Both A and R are true and R is the correct explanation for A
b) Both A and R are true and R is not the correct explanation for A
c) A is true but R is false
d) A is false but R is true.
Ans: C
The assertion is correct, but the reason is incorrect. The resistance of a wire is directly proportional to its length, not inversely proportional. This means that a longer wire will have a greater resistance because the electrons travelling through it will encounter more collisions and therefore more resistance.

Q3: The following questions consists of two statements –Assertion(A) and Reason (R). Answer these questions selecting the appropriate option given below.
Assertion (A): A cell converts chemical energy into electrical energy.
Reason(R): A cell maintains a potential difference across its terminals due to chemical reactions.
a) Both A and R are true and R is the correct explanation for A
b) Both A and R are true and R is not the correct explanation for A
c) A is true but R is false
d) A is false but R is true.
Ans: B
The assertion and reason are both correct, but the reason is not explaining the assertion. A cell does convert chemical energy into electrical energy through chemical reactions, and it also maintains a potential difference across its terminals due to these reactions. However, the reason is not explaining the process of energy conversion but is stating another fact about a cell.

Q4: The following questions consists of two statements –Assertion(A) and Reason (R). Answer these questions selecting the appropriate option given below.
Assertion (A): Alloys are commonly used in electrical heating devices.
Reason(R): Alloys do not oxidize at high temperatures.
a) Both A and R are true and R is the correct explanation for A
b) Both A and R are true and R is not the correct explanation for A
c) A is true but R is false
d) A is false but R is true.
Ans: A
Both the assertion and the reason are correct and the reason is the correct explanation for the assertion. Alloys are used in electrical heating devices because they do not oxidize (burn) at high temperatures. This is a desirable property for heating elements because it extends their lifespan and maintains their efficiency.

Q5: The following questions consists of two statements –Assertion(A) and Reason (R). Answer these questions selecting the appropriate option given below.
Assertion (A): When resistances are connected between the same two points they are said to be in series.
Reason(R): When resistors are connected in series the current through each resistor is the same.
a) Both A and R are true and R is the correct explanation for A
b) Both A and R are true and R is not the correct explanation for A
c) A is true but R is false
d) A is false but R is true.
Ans: D
The assertion is incorrect while the reason is correct. When resistances are connected end-to-end, they are said to be in series. However, the statement that resistors are said to be in series when connected between the same two points is incorrect. The correct reason is that when resistors are connected in series, the same current flows through each resistor because they share the same path.

Very Short Answers

Q1: Define resistance. Give its S.I. unit.

Ans: Resistance is the property of a conductor to oppose the flow of charges through it. SI unit of resistance is Ohm (Ω).  

Q2: What will happen to the resistivity of a wire of length L if it is cut into three parts?
Ans: Resistivity of the wire will not change even when the wire is cut into three parts as resistivity is a characteristic of the material of the conductor and does not depend on the physical dimensions of the conductor.

Q3: The potential difference across the wire having fixed resistance is tripled. By how much does the electric power increase?
Ans: The electric power will increase by nine times when the potential difference across the wire having fixed resistance is tripled. According to Ohm’s law, potential difference V is proportional to current, I. Therefore, when V is made 3 times, I will increase 3 times. As Power P = VI, therefore, Power will increase by 9 times. 

Q4: Is electric potential a scalar or a vector quantity ?
Ans: Electric potential is a scalar quantity. 

Q5: What causes the potential difference between the two terminals of a cell?
Ans: Excess of electrons at the negative terminal and lack of electrons at the positive terminal (due to chemical reactions) causes potential difference between the two terminals of a cell.  

Q6: Define 1 Coulomb.
Ans: Q=ne
Q= charge = 1 C
1C = n×e 1c is that charge which contains 6.25 x 1018 number of electrons in it.

Q7: Calculate the number of electrons in 5C charge?
Ans: Given Q= 5C , find n=? As we know Q=ne 5=n×1.6×10^-19C N= 5/1.6×10^-19
N= 3.12× 10^-18

Q8: What is a good conductor?
Ans: Good conductors are substances that offer little resistance to current flowing through them. Examples - Silver, Copper, Gold, Aluminium. Poor conductors are substances that offer a lot of resistance, hence preventing the current from flowing through it.

Q9: Is human body an insulator or conductor?
Ans: Skin is actually a very good insulator as well so, relative to metal, humans aren't very good conductors. However, it is things such as the ionized water and whatnot that make up our body that do cause us to conduct. Actually the body is not too good.

Short Answers Type Questions

Q1:  Find the minimum rating of fuse that can be safely used on a line on which two 1.1 KW electric geysers are to run simultaneously.
The supply voltage is 220 V.
Ans: Power P = VI. As the two geysers have power rating 1.1 kW or 1100 W and are connected in parallel, each geyser draws a current I = P/V =
1100/220 A = 5 A. 

Q2: The electric power consumed by a device may be calculated by either of the two expressions P = I2R or P = V2/R. The frist expression indicates that it is directly proportional to R whereas the second expression indicates inverse proportionality. How can the seemingly different dependence of P on R in these expressions be explained?
Ans:  The expression P = I2R is used for calculating electric power when only current I and resistance R are known, whereas P = V2/R is used for calculating power when voltage V and resistance R are known.

Q3: Why does the cord of an electric heater does not glow while heating element does?
Ans: Heating effect = I2Rt
where I is the current flowing and R is the resistance and t is the time. Current is same in cord and in heating element. Resistance R of the cord is negligible since it is made of copper (which has very less resistivity) while heating element is made in nichrome whose resistivity is 6,000 times more than copper. Nichrome gets heated up much more than copper.

Q4: How will the heat produced in a resistor R change if its resistance is reduced to half of its initial value, other parameters of the circuit remain unchanged?
Ans: The heat produced in a resistor R is given by Joule’s law of heating H = I2Rt, where I is the current and t is the time. When R becomes R/2, I will become 2I according to Ohm’s law.
Therefore, heat produced = (2I)2(R/2)t = 2H. The heat produced will become double.

Q5: Why is parallel arrangement used in domestic wiring? 
Ans:  Parallel arrangement is used in domestic wiring due to the following reasons:

• Each device will have the same voltage which is equal to the voltage of the supply.
• If two or more devices are used at the same time, then each appliance will be able to draw the required current.
• If one of the devices fails, then the other keeps working.

Q6: (A) What is the resistance of a conductor?
(B) What happens to the electrical resistance when mercury is cooled to 4.12 k?
(C) What name is given to this phenomenon?
Ans:  (A) The property of a conductor due to which it opposes the flow of current through it is called resistance. The resistance of a conductor is numerically equal to the ratio of potential difference across its ends to the current flowing through it.
(B) When mercury is cooled to 4.12 K, the electrical resistance of mercury disappears completely and becomes zero and the mercury becomes super conductor.
(C) This phenomenon of loss of electrical resistance of a substance on cooling it to an extremely low temperature is known as superconductivity.

Q7: Draw a circuit diagram having the following components:
(a) Bulb
(b) A two cell battery
(c) Ammeter
(d) A closed key
Ans:

Long Answers Type Questions

Q1: Answer the following:
(A) Why ammeter is always connected in series?
(B) give dry cells each of 1.0 volt have internal resistance of 0.2, 0.3, 0.4, 0.5 and 1.2 ohms. When connected in series, what current will these five cells furnish through 10 ohm resistance?
Ans:  (A) An ammeter is used to measure the current flowing through a circuit. We know that current remains same in series connection. lso the resistance of an ammeter is verysmall due to which it doesn’t affect the current to be measured. So, an ammeter is always connected in series to measure current.
(B) Total voltage produced by the batteries
V = 5 x 1.5 = 7.5 V
Total resistance
R = R1 + R2 + R3 + R4 + R5
R = (0.2 + 0.3 + 0.4 + 0.5 + 1.2) + 10
= 12.6 W
Therefore, current
I  = V/R
= 7.5/12.6 = 0.595 A.

Q2: For the circuit shown in the given diagram:
What is the value of
i. current through 6 resistor?
ii. potential difference across 12 resistor?
Ans:  Let the current through the circuit be I which is divided into I1 and I2 in the arms AB and CD respectively, then we have
I = I1 + I2
In the arm AB, the total resistance is
R1 =  6Ω + 3Ω = 9Ω
and the total resistance in the arm CD is
R2   = 12Ω + 3Ω = 15Ω
i. Then current in the 6Q resistor i.e.,

Q3: List two distinguishing features between the resistance and resistivity of a conductor. A wire is stretched so that its length becomes 6/5 times of its original length. If its original resistance is 25 W, find its new resistance and resistivity. Give justification for your answer in each case.
Ans: Resistance
(i) It is the ratio of voltage over current at a particular temperature.
(ii) Its S.I. unit is ohm.
(iii) It is the property of a conductor
Resistivity
(i) It is the resistance of a wire of length 1 m and area of cross section 1 m2.
(ii) Its S.I. unit is ohm metre
(iii) It is the property of the material of the conductor
Since resistance is directly proportional to the length and is inversely proportional to the area of cross section.
∴ New Resistance:

When the wire is stretched, its length becomes 6/5 times of its original length, and area of cross-section will become 5/6. Resistivity will remain the same because it does not depend upon the length and area of cross section. It depends on the nature of material of the substance and the temperature.

Q4: (i) Write an expression for the resistivity of a substance.
(ii) State the SI unit of resistivity.
(iii) Distinguish between resistance and resistivity.
(iv) Name two factors on which the resistivity of a substance depends and two factors on which it does not depend.
Ans: (i) Resistivity (r) = RA/l
(ii) Its SI unit is W m.
(iii) Resistivity is a characteristic property of a material that does not depend upon the dimensions of
the material whereas resistance depends upon the dimensions of the material.
(iv) Resistivity does not depend on the:
(a) length of conductor, (b) area of cross section of conductor Resistivity depends on the:
(a) nature of material of conductor (b) temperature of conductor

Q5: The potential difference between the terminals of an electric heater is 60 V when it draws a current of 4 A from the source. What current will the heater draw if the potential difference is increased upto 120 V?
Ans: 12. V = 60 V, I = 4 A
R = V/I = 60/4 = 15Ω [By Ohm's Law; V = IR]
Now, V = 120 V, I = ? R = 15 Ω
I = V/R = 120/15 = 8A

Q6: State Ohm’s law. Draw a labelled circuit diagram to verify this law in the laboratory. If you draw a graph between the potential difference and current flowing through a metallic conductor, what kind of curve will you get? Explain how would you use this graph to determine the resistance of the conductor.
Ans: Ohm’s Law: It states that ratio of potential difference and current is constant and is equal to the
resistance of the conductor at a particular temperature. In other words, the current flowing through a
conductor is directly proportional to the potential difference at a constant temperature.
The graph between V and I will be a straight line.
Slope = tan θ = ‘R’
Slope = BC/AC = R