WBBSE Class 10 Physical Science Notes Chapter 6 (Current Electricity ) in English | Class 10 Current Electricity Notes
Class 10 Current Electricity Notes
Very Short Answer Type Questions:
**Question 1.**
*What is electric current?*
**Answer:**
Electric current is the flow of electrons, ions, or any electrically charged particles through a medium.
**Question 2.**
*What are conductors?*
**Answer:**
Conductors are substances that allow electric charge to flow easily.
**Question 3.**
*What are non-conductors?*
**Answer:**
Non-conductors, or insulators, are substances that do not allow electric charge to pass through them.
**Question 4.**
*How can we define electric current in a quantitative way?*
**Answer:**
In a quantitative way, electric current is defined as the rate of flow of electric charge through any cross-section of a conductor per unit time.
**Question 5.**
*What do you mean by D.C.?*
**Answer:**
D.C. stands for Direct Current, where the electric current always flows in the same direction.
**Question 6.**
*What do you mean by A.C.?*
**Answer:**
A.C. stands for Alternating Current, where the direction of current alternates periodically from one direction to the opposite direction.
**Question 7.**
*What is an electric cell?*
**Answer:**
An electric cell is a device in which electrical energy is obtained from chemical energy.
**Question 8.**
*What is the negative electrode?*
**Answer:**
The metal rod with an excess of negative charge is called the negative electrode of a cell.
**Question 9.**
*What is the positive electrode?*
**Answer:**
The metal rod with an excess of positive charge is called the positive electrode.
**Question 10.**
*What is an open circuit?*
**Answer:**
An open circuit occurs when the electrodes of a cell are not connected by a conductor externally.
**Question 11.**
*What is a closed circuit?*
**Answer:**
A closed circuit occurs when the electrodes are connected internally with a conductor.
**Question 12.**
*What is emf of a cell?*
**Answer:**
The potential difference between the electrodes of a cell in an open circuit is called emf (electromotive force).
**Question 13.**
*What is the direction of current in the external circuit of a cell?*
**Answer:**
Current flows from the positive electrode to the negative electrode in the external circuit of a cell.
**Question 14.**
*What is the emf of a simple voltaic cell?*
**Answer:**
The emf of a simple voltaic cell is 1.08 volts.
**Question 15.**
*What is the physical nature of electromotive force?*
**Answer:**
Electromotive force is a form of energy.
**Question 16.**
*What is the unit of charge in the SI system?*
**Answer:**
The unit of charge in the SI system is the coulomb (C).
**Question 17.**
*What is the SI unit of current strength?*
**Answer:**
The SI unit of current strength is the ampere (A).
**Question 18.**
*What are the units of electromotive force and potential difference in the SI system?*
**Answer:**
The SI unit of both electromotive force and potential difference is the volt (V).
**Question 19.**
*What is the SI unit of resistance?*
**Answer:**
The SI unit of resistance is the ohm (Ω).
**Question 20.**
*State the cases in which Ohm’s law is not valid.*
**Answer:**
Ohm’s law is not valid for current flowing through gases under low pressure, electrolytes, and semiconductors.
**Question 21.**
*How does the resistance of a conductor depend on the cross-section of the conductor?*
**Answer:**
The resistance of the conductor decreases with an increase in cross-section.
**Question 22.**
*In a system of resistors connected in parallel, how is the magnitude of the equivalent resistance related to the magnitude of the resistor of least value?*
**Answer:**
The equivalent resistance is smaller than the resistance of the smallest resistor.
**Question 23.**
*How is the heat generated due to electric current through a resistor related to the strength of the current?*
**Answer:**
The heat generated is directly proportional to the square of the current.
**Question 24.**
*How is the heat generated due to electric current in a resistor related to the resistance of the resistor?*
**Answer:**
The heat generated is directly proportional to the resistance.
**Question 25.**
*What is 1 B.O.T.?*
**Answer:**
1 B.O.T. (Board of Trade unit) is the total electric energy expended in 1 hour at the rate of 1 kilowatt.
**Question 26.**
*Which energy is converted to which other in an electric motor?*
**Answer:**
In an electric motor, electric energy is converted to mechanical energy.
**Question 27.**
*What is earthing?*
**Answer:**
Earthing is the process of connecting the metal case of an electrical appliance to the earth with the help of a metal wire.
**Question 28.**
*What is the usual colour of a live wire?*
**Answer:**
The usual colour of a live wire is red.
**Question 29.**
*What is the usual colour of a neutral wire?*
**Answer:**
The usual colour of a neutral wire is black.
**Question 30.**
*What is the usual colour of the earthing wire?*
**Answer:**
The usual colour of the earthing wire is green.
**Question 31.**
*Which effect of electric current is demonstrated in an electromagnet?*
**Answer:**
The magnetic effect.
**Question 32.**
*How is current related to potential difference?*
**Answer:**
Current is directly proportional to potential difference.
**Question 33.**
*What is the unit of resistivity in the CGS system?*
**Answer:**
The unit of resistivity in the CGS system is ohm-centimeter (Ohm-Cm).
**Question 34.**
*Current flows through a conductor from east to west; in which direction do electrons flow through it?*
**Answer:**
Electrons flow from west to east.
**Question 35.**
*What is an electromagnet?*
**Answer:**
An electromagnet is a temporary magnet produced by passing electric current through an insulated copper wire coiled around a soft iron body.
**Question 36.**
*What is the core of an electromagnet?*
**Answer:**
The soft iron body around which an insulated copper wire is coiled is called the core of the electromagnet.
**Question 37.**
*Mention two uses of an electromagnet.*
**Answer:**
An electromagnet is used in an electric calling bell and an electric motor.
**Question 38.**
*What happens if the soft iron used in the electromagnet of an electric bell is replaced with steel?*
**Answer:**
The bell will not work, as the steel body turns into a permanent magnet.
**Question 39.**
*How does the strength of an electromagnet depend on the number of turns of a solenoid?*
**Answer:**
The strength of an electromagnet increases with the number of turns of an insulated wire per unit length of a solenoid.
**Question 40.**
*What is the function of an electric switch?*
**Answer:**
An electric switch is used to stop or allow the flow of electric current to an electric appliance as and when needed.
**Question 41.**
*What is a voltmeter?*
**Answer:**
A voltmeter is used to measure the potential difference between two points in a section of an electrical circuit.
**Question 42.**
*What is an ammeter?*
**Answer:**
An ammeter is used to measure the current flowing through an electric circuit.
**Question 43.**
*What should be the resistance of an ideal ammeter?*
**Answer:**
Ideally, the resistance of an ammeter should be zero.
**Question 44.**
*What should be the resistance of an ideal voltmeter?*
**Answer:**
Ideally, the resistance of a voltmeter should be infinity.
**Question 45.**
*What are the metals used to prepare fuse wire?*
**Answer:**
Fuse wires are usually made of an alloy of lead (75%) and a small amount of tin (25%).
**Question 46.**
*What is the rating of a fuse wire?*
**Answer:**
The rating of a fuse wire is the maximum current that may be allowed to flow through it before it melts.
**Question 47.**
*What is the nature of the electric charge on an ebonite rod when it is rubbed with cat skin?*
**Answer:**
The ebonite rod becomes negatively charged.
**Question 48.**
*A glass rod is rubbed with silk. What type of charges do they acquire?*
**Answer:**
The glass rod becomes positively charged, and the silk becomes negatively charged.
**Question 49.**
*What is the SI unit of electric charge?*
**Answer:**
The SI unit of electric charge is the coulomb (C).
**Question 50.**
*What is the least value of electric charge available?*
**Answer:**
The least value of electric charge available is \(1.6 \times 10^{-19} C\).
Short Answer Type Questions:
**Question 1.**
*What do you mean by potential difference?*
**Answer:**
Potential difference refers to the electrical condition of a point in an electric field or on a current-carrying conductor. It indicates whether electrons will flow from it or towards it from another connected point.
**Question 2.**
*What is the definition of coulomb?*
**Answer:**
Coulomb is the quantity of electric charge that, when passing through a silver nitrate solution during electrolysis, deposits 0.001118 g of silver at the cathode.
**Question 3.**
*What is the definition of ampere?*
**Answer:**
Ampere is the current that, when flowing through a silver nitrate solution during electrolysis for one second, deposits 0.001118 g of silver at the cathode.
**Question 4.**
*What is the definition of ohm?*
**Answer:**
Ohm is the resistance of a conductor when one ampere of current flowing through it establishes a potential difference of one volt between its two ends.
**Question 5.**
*State Ohm’s law.*
**Answer:**
Ohm’s law states that, with temperature and physical conditions remaining constant, the current flowing between any two points of a conductor is proportional to the potential difference between them.
**Question 6.**
*Deduce the mathematical form of Ohm’s law.*
**Answer:**
The mathematical form of Ohm’s law is given by \(V = IR\), where \(V\) is the potential difference, \(I\) is the current, and \(R\) is the resistance of the conductor.
**Question 7.**
*What is the definition of resistance from Ohm’s law?*
**Answer:**
The definition of resistance from Ohm’s law is that the resistance of a conductor is the ratio of the potential difference between its ends to the current flowing through it.
**Question 8.**
*On what factors does the resistance of a conductor depend?*
**Answer:**
The resistance of a conductor depends on its length, cross-sectional area, and the material from which it is made.
**Question 9.**
*What is specific resistance?*
**Answer:**
Specific resistance, or resistivity (\(\rho\)), is the constant of proportionality in the relationship between the resistance, length, and cross-sectional area of a conductor. It is the resistance of a conductor of length 1 meter and area of cross-section 1 m².
**Question 10.**
*Specific resistance of copper at 20°C is \(1.6 \times 10^{-6}\) ohm-cm, what does it mean?*
**Answer:**
It means that the resistance across the opposite faces of a copper cube with a side length of 1 cm, at 20°C, is \(1.6 \times 10^{-6}\) ohms.
**Question 11.**
*What do you mean by combination of resistance?*
**Answer:**
Combination of resistance refers to the arrangement of multiple resistances in an electrical circuit. Two common types are series combination and parallel combination.
**Question 12.**
*Define equivalent resistance.*
**Answer:**
Equivalent resistance is the single resistance that, when substituted for multiple resistances in a circuit, keeps the voltage and current unchanged.
**Question 13.**
*What do you mean by series combination?*
**Answer:**
In series combination, resistances are connected end-to-end, and the same current flows through all resistances. The equivalent resistance (\(R\)) in a series combination is the sum of individual resistances.
**Question 14.**
*What do you mean by parallel combination?*
**Answer:**
Parallel combination involves placing resistors side by side with corresponding ends joined together. The equivalent resistance (\(R\)) in a parallel combination is given by \( \frac{1}{R} = \frac{1}{r_1} + \frac{1}{r_2} + \frac{1}{r_3} \).
**Question 15.**
*What is internal resistance of a cell?*
**Answer:**
Internal resistance is the small resistance offered by the electrolyte of a cell to the electric charges flowing through it from the negative to the positive plate.
**Question 16.**
*What is watt-hours? Whose unit is it?*
**Answer:**
Watt-hours is the unit of electrical energy. It represents the energy consumed when an electrical machine with a power of one watt operates for one hour.
**Question 17.**
*Define 1 kilowatt-hour?*
**Answer:**
One kilowatt-hour is the amount of energy consumed when a machine of 1 kilowatt power operates for one hour. It is also known as a Board of Trade Unit (B.O.T. unit).
**Question 18.**
*Why is nichrome wire used in electrically heated appliances?*
**Answer:**
Nichrome wire is used in electrically heated appliances because it has much larger resistance than copper, producing a significant amount of heat when electricity
flows through it. It does not melt or oxidize even at high temperatures.
**Question 19.**
*What is short circuiting and what is overloading?*
**Answer:**
- **Short Circuiting:** Direct connection between the two terminals of a power source or through a low-resistance metallic wire. It leads to overheating, melting, and disruption of the circuit.
- **Overloading:** Drawing excessive current when multiple high-powered electrical appliances are switched on simultaneously.
**Question 20.**
*What is a fuse? What is fuse rating?*
**Answer:**
- **Fuse:** A thin wire made of an alloy of lead (75%) and tin (25%), placed in a china clay insulator box, used for safety in electrical circuits. It melts when there is a surge in current, cutting off the circuit.
- **Fuse Rating:** The maximum current that a fuse wire can allow to flow through it before melting is called the fuse rating.
**Question 21.**
*What is earthing? How does it protect against electric shock?*
**Answer:**
- **Earthing:** Connecting the metal case of an electrical appliance to the earth with a metal wire.
- **Protection:** If a live wire accidentally touches the metal body of an appliance, the current flows directly to the earth through the earth wire, preventing electric shock.
**Question 22.**
*What is Oersted’s experiment?*
**Answer:**
Oersted’s experiment involves observing the deflection of a freely rotating magnetic needle when a current-carrying conductor is held above and parallel to it. The magnetic needle deflects due to the flow of current.
**Question 23.**
*State Ampere’s swimming rule.*
**Answer:**
Ampere’s swimming rule states that if a man is imagined to be swimming along a current-carrying wire in the direction of the current (south to north) with his face turned towards a freely rotating magnetic needle, then the north pole of the needle will be deflected towards his left hand.
**Question 24.**
*State Fleming’s left hand rule.*
**Answer:**
Fleming’s left hand rule states that if the thumb, the first finger, and the middle finger of the left hand are held mutually perpendicular to each other, with the first finger pointing in the direction of the magnetic field and the second finger to that of the current, then the thumb will indicate the direction of motion of the conductor.
**Question 25.**
*How can the direction of rotation of Barlow’s wheel be changed?*
**Answer:**
The direction of rotation of Barlow’s wheel can be changed by reversing either the direction of current or the direction of the magnetic field.
**Question 26.**
*On what factors does the speed of rotation of Barlow’s wheel depend?*
**Answer:**
The speed of rotation of Barlow’s wheel depends on the current flowing through it, the intensity of the magnetic field, and whether the current is direct or alternating.
**Question 27.**
*How can the direction of rotation of Barlow’s wheel be changed?*
**Answer:**
The direction of rotation of Barlow’s wheel will reverse if either the direction of current or the direction of the magnetic field is reversed. If both are reversed, the direction of rotation remains unchanged.
**Question 28.**
*A bulb is marked ‘230 V-60 W’, what does it indicate?*
**Answer:**
The marking on the bulb indicates that when the bulb is used in an electrical line with a potential difference of 230 volts, it will consume electrical energy at a rate of 60 joules per second.
**Question 29.**
*What do you mean by the statement, ‘Potential difference between two points in an electric field is 5 volts’?*
**Answer:**
The statement indicates that an external agent has to do 5 joules of work to carry 1 coulomb of positive charge from a point at lower potential to a point at higher potential in the electric field.
**Question 30.**
*Why is resistivity also called specific resistance?*
**Answer:**
Resistivity is also called specific resistance because it represents the resistance of a material of specified dimensions (length 1 meter, area of cross-section 1 m²). It is specific to the material and is independent of the quantity of the material.
Numerical Problems:
**Example 1:**
*The resistance of a conductor is 100 ohms, and a current of 5 amperes is flowing through it. What will be the potential difference at the two ends of the conductor?*
**Answer:**
Given:
- Resistance (\(R\)) = 100 ohms
- Current (\(I\)) = 5 amperes
Using Ohm's law: \(V = RI\)
\[ V = 100 \, \text{ohms} \times 5 \, \text{amperes} = 500 \, \text{volts} \]
**Example 2:**
*A current of 2 amperes flows through a conductor. The potential difference across the conductor is 50 volts. What is the resistance?*
**Answer:**
Given:
- Current (\(I\)) = 2 amperes
- Potential difference (\(V\)) = 50 volts
Using Ohm's law: \(R = \frac{V}{I}\)
\[ R = \frac{50 \, \text{volts}}{2 \, \text{amperes}} = 25 \, \text{ohms} \]
**Example 3:**
*10 amperes of current is allowed through a conductor for 1 minute. Find the amount of charge flown.*
**Answer:**
Given:
- Current (\(I\)) = 10 amperes
- Time (\(t\)) = 1 minute = 60 seconds
The charge (\(Q\)) is given by \(Q = I \times t\)
\[ Q = 10 \, \text{amperes} \times 60 \, \text{seconds} = 600 \, \text{coulombs} \]
**Example 4:**
*Potential difference across two points of a conductor is 60 volts. The resistance of the conductor is 10 ohms. Find the current through the conductor.*
**Answer:**
Given:
- Potential difference (\(V\)) = 60 volts
- Resistance (\(R\)) = 10 ohms
Using Ohm's law: \(I = \frac{V}{R}\)
\[ I = \frac{60 \, \text{volts}}{10 \, \text{ohms}} = 6 \, \text{amperes} \]
**Example 5:**
*A current of 2 amperes is passed through a conductor of resistance 4 ohms. Find the potential difference across the conductor.*
**Answer:**
Given:
- Current (\(I\)) = 2 amperes
- Resistance (\(R\)) = 4 ohms
Using Ohm's law: \(V = I \times R\)
\[ V = 2 \, \text{amperes} \times 4 \, \text{ohms} = 8 \, \text{volts} \]
**Example 6:**
*Resistance of one conductor is double that of the other. What will be the ratio of current through these two conductors if they are subjected to the same potential difference?*
**Answer:**
Let the resistances of the conductors be \(R\) and \(2R\) and the potential difference be \(V\). The ratio of current (\(I_1\) and \(I_2\)) through the conductors is given by:
\[ \frac{I_1}{I_2} = \frac{1}{2} \]
**Example 7:**
*2 units of current are flowing through a conductor of 4 ohms. What is the potential difference at the ends of the conductor?*
**Answer:**
Given:
- Current (\(I\)) = 2 amperes
- Resistance (\(R\)) = 4 ohms
Using Ohm's law: \(V = I \times R\)
\[ V = 2 \, \text{amperes} \times 4 \, \text{ohms} = 8 \, \text{volts} \]
**Example 8:**
*The resistance per meter of a wire is 1.2 ohms, and its specific resistance is \(60.28 \times 10^{-8}\) ohm-m. Find the radius of the wire.*
**Answer:**
Given:
- Resistance per meter (\(R\)) = 1.2 ohms
- Specific resistance (\(\rho\)) = \(60.28 \times 10^{-8}\) ohm-m
The area of cross-section (\(A\)) is given by \(A = \frac{\rho \times l}{R}\), where \(l = 1\) meter.
\[ A = \frac{(60.28 \times 10^{-8}) \times 1}{1.2} = 50.2 \times 10^{-8} \, \text{m}^2 \]
If \(r\) is the radius of the wire, then \(A = \pi r^2\).
\[ \pi r^2 = 50.2 \times 10^{-8} \, \text{m}^2 \]
\[ r^2 = \frac{50.2 \times 10^{-8}}{\pi} \]
\[ r \approx 0.04 \, \text{cm} \]
**Example 9:**
*There are two copper wires of equal length. The radius of one is twice the other. Find the ratio of their resistances.*
**Answer:**
Let the radii of the wires be \(r\) and \(2r\). The ratio of their resistances (\(R_1\) and \(R_2\)) is given by:
\[ \frac{R_1}{R_2} = \left(\frac{r}{2r}\right)^2 = \frac{1}{4} \]
**Example 10:**
*The resistivity of a substance is \(9 \times 10^{-8}\) ohm-m. What length of the wire of that material, having a diameter of 0.3 cm, will give a resistance of 100 ohms?*
**Answer:**
Given:
- Resistivity (\(\rho\)) = \(9 \times 10^{-8}\) ohm-m
- Resistance (\(R\)) = 100 ohms
- Diameter (\(D\)) = 0.3 cm
The area of cross-section (\(A\)) is given by \(A = \frac{\pi D^2}{4}\).
\[ A = \frac{\pi \times (0.3)^2}{4} \]
The length (\(l\)) of the wire is given by \(l = \frac{R \times A}{\rho}\).
\[ l = \frac{100 \times \frac{\pi \times (0.3)^2}{4}}{9 \times 10^{-8}} \]
**Example 11:**
*The resistance of a wire of cross-sectional area 0.01 cm² is 10 ohms. What is the length of the wire? The specific resistance of the wire is \(50 \times 10^{-6}\) oh
m-cm.*
**Answer:**
Given:
- Resistance (\(R\)) = 10 ohms
- Cross-sectional area (\(A\)) = 0.01 cm²
- Specific resistance (\(\rho\)) = \(50 \times 10^{-6}\) ohm-cm
The length (\(l\)) of the wire is given by \(l = \frac{R \times A}{\rho}\).
\[ l = \frac{10 \times 0.01}{50 \times 10^{-6}} = 2000 \, \text{cm} \]
**Example 12:**
*The length and area of cross-section of a wire are double that of another wire of the same material. Find the ratio of their resistances.*
**Answer:**
Let the length of the wires be \(2l\) and \(l\) and their areas of cross-section be \(2A\) and \(A\) respectively. The ratio of their resistances (\(R_1\) and \(R_2\)) is given by:
\[ \frac{R_1}{R_2} = \frac{\rho \times 2l \times 2A}{\rho \times l \times A} = \frac{4lA}{lA} = 4 \]
**Example 13:**
*Find the specific resistance of the material of a wire of length 100 cm, area of cross-section 0.2 cm², and resistance 2 ohms.*
**Answer:**
Given:
- Length (\(l\)) = 100 cm
- Cross-sectional area (\(A\)) = 0.2 cm²
- Resistance (\(R\)) = 2 ohms
The specific resistance (\(\rho\)) is given by \(\rho = \frac{R \times A}{l}\).
\[ \rho = \frac{2 \times 0.2}{100} = 0.004 \, \text{ohm-cm} \]
**Example 14:**
*Three resistors of 1 ohm, 2 ohms, and 3 ohms are connected in parallel. What will be their equivalent resistance?*
**Answer:**
For parallel combination, the equivalent resistance (\(R_{\text{eq}}\)) is given by:
\[ \frac{1}{R_{\text{eq}}} = \frac{1}{1} + \frac{1}{2} + \frac{1}{3} \]
\[ R_{\text{eq}} = \frac{1}{\frac{1}{1} + \frac{1}{2} + \frac{1}{3}} \]
**Example 15:**
*Three wires of resistance 2 ohms, 3 ohms, and 5 ohms are connected in series with a cell of emf 5 volts. What will be the current through each wire?*
**Answer:**
For series combination, the equivalent resistance (\(R_{\text{eq}}\)) is given by:
\[ R_{\text{eq}} = R_1 + R_2 + R_3 = 2 + 3 + 5 = 10 \, \text{ohms} \]
Using Ohm's law, \(I = \frac{V}{R}\), the current (\(I\)) through each wire is given by:
\[ I = \frac{5}{10} = 0.5 \, \text{amperes} \]
