Metals are good conductors of electricity because they have a large number of free electrons (also called conduction electrons). These electrons are not tightly bound to atoms and can move freely through the metal. When a potential difference is applied, these free electrons flow easily, allowing electric current to pass.
Glass is a bad conductor (insulator) because its electrons are tightly bound to their atoms. It does not have free electrons available to move and carry electric current. As a result, electricity cannot flow through it easily.
In short:
- Metals have free-moving electrons ---> Good conductors.
- Glass lacks free-moving electrons ----> Bad conductor.
More Questions on Electricity
An electric heater with a power rating of 2 kW is operated for 3 hours daily for the entire month of April. If the cost of electricity is Rs 6 per unit, what is the total electricity bill for the month? (Assume April has 30 days)
→ 2Assertion (A): Tungsten metal is used for making the filament of incandescent electric lamps. Reason (R): Tungsten has a very high melting point and produces light at high temperatures without melting.
→ 3Explain why the main power supply line coming into a house typically uses a thicker gauge copper wire compared to the thinner wires used for individual appliance connections within the house.
→ 4Two electric bulbs, rated 100W, 220V and 60W, 220V respectively, are connected in series to a 220V supply. Which bulb will glow brighter and why?
→ 5A circuit consists of three resistors: R1, R2, and R3. R1 = 5 Ω is connected in series with the parallel combination of R2 = 10 Ω and R3 = 10 Ω. If this circuit is connected to a 12V battery, what is the power dissipated across R1?
→ 6Explain why household electrical appliances are always connected in parallel with the main supply and not in series.
→ 7Assertion (A): Nichrome alloy is extensively used in the heating elements of electrical appliances like toasters and electric irons. Reason (R): Nichrome has a very high resistivity and a high melting point, making it suitable for producing significant heat without melting.
→ 8An electric heater is rated at 2.2 kW and operates on a 220 V household supply. What is the minimum rating of the fuse that should be used in the circuit to protect the heater?
→ 9A metallic wire of resistance R is stretched uniformly so that its new length becomes twice its original length. Assuming that its volume remains constant during stretching, what will be its new resistance?
→ 10A household circuit consists of two resistors, R1 = 6 Ω and R2 = 3 Ω, connected in parallel. This parallel combination is then connected in series with a third resistor, R3 = 8 Ω. If the entire circuit is connected to a 20 V battery, what is the current flowing through resistor R2?
→ 11The resistance of a circuit component is constant. If the voltage across it is halved, the current through it will:
→ 12The resistance of a conductor is 5 Ohm. If a current of 2A flows through it, the potential difference across its ends is:
→ 13A conductor has 10²0 free electrons passing through a cross-section in 2 seconds. The current flowing is:
→ 14If the voltage across a resistor is 10V and the current flowing is 2A, the power dissipated by the resistor is:
→ 15Which of the following is not a property of electric field lines?
→ 16How many joules are there in 1 calorie?
→ 17The formula for electric energy consumed (E) is:
→ 18A 100W bulb and a 40W bulb are connected in parallel to a 220V supply. Which bulb will glow brighter?
→ 19A 100W bulb and a 40W bulb are connected in series to a 220V supply. Which bulb will glow brighter?
→ 20Which of these is the most suitable material for a heating element?
→ 21What happens to the resistance of a conductor if its area of cross-section is increased?
→ 22The reciprocal of resistance is called:
→ 23In a parallel circuit, if one bulb fuses, the other bulbs:
→ 24In a series circuit, if one bulb fuses, the other bulbs:
→ 25Which combination of resistors provides the lowest equivalent resistance?
→ 26An electric iron of 1000 W is used for 2 hours daily. If the cost of 1 unit of electricity is Rs. 5, what is the cost of using the iron for 30 days?
→ 27What is the equivalent resistance of three 6 Ohm resistors connected in parallel?
→ 28What is the total power consumed by two lamps rated 60W and 40W, respectively, when connected in parallel across a 220V supply?
→ 29The resistance of a wire is R. If it is stretched to twice its original length, its new resistance will be:
→ 30If the current through a resistor is doubled, the heat produced in a given time interval will:
→ 31A 2 Ohm resistor carries a current of 3 A. The heat produced in 10 seconds is:
→ 32Which of the following is an ohmic conductor?
→ 33If the temperature of a semiconductor increases, its resistance:
→ 34The direction of electron flow is ___________ to the conventional current.
→ 35The energy supplied by the cell in moving a unit charge from one end to the other is called its:
→ 36What is the cause of 'overloading' in domestic circuits?
→ 37What does a 'short circuit' mean in an electric circuit?
→ 38The symbol for a variable resistor is:
→ 39Why are copper wires generally used for electrical transmission?
→ 40If an electric bulb of 40W, 220V is connected to a 110V supply, the power consumed will be:
→ 41Which statement is true for voltage in a parallel circuit?
→ 42Which statement is true for current in a series circuit?
→ 43A device that changes the resistance in an electric circuit is called a:
→ 44The material of an electric fuse wire should have:
→ 45What is the effect of increasing temperature on the resistance of a pure metal conductor?
→ 46An electric cell converts:
→ 47Which of the following is true about electric potential?
→ 48The property of a conductor to resist the flow of current is called:
→ 49In a parallel circuit containing two resistors, if the current through the first resistor is 2 A and the total current is 5 A, what is the current through the second resistor?
→ 50A circuit consists of two resistors in series. If the voltage across the first resistor is 5 V and the total voltage is 12 V, what is the voltage across the second resistor?
→ 51If an electric bulb draws a current of 0.5 A when the voltage is 200 V, its power is:
→ 52If the reading of an ammeter is 2 A and the resistance is 10 Ohm, what is the voltage across the resistor?
→ 53A 60 W light bulb is switched on for 2 hours. How much electrical energy is consumed?
→ 54Which of the following represents electric power?
→ 55To increase the brightness of a bulb in a circuit, we can:
→ 56The resistance of an ideal voltmeter is:
→ 57The resistance of an ideal ammeter is:
→ 58Why is tungsten used for the filament of incandescent light bulbs?
→ 59Which material is typically used for heating elements in electric toasters and irons?
→ 60A component whose resistance changes with voltage is called a:
→ 61A current of 2 A flows through a conductor for 5 minutes. The amount of charge that passes through the conductor is:
→ 62The amount of current flowing through a circuit is 0.5 A. How much charge passes through a point in the circuit in 10 minutes?
→ 63If 100 J of work is done to move 4 C of charge from one point to another, the potential difference between the two points is:
→ 64What is the potential difference required to make 1 A of current flow through a resistance of 1 Ohm?
→ 65Which of the following is a good conductor of electricity?
→ 66The 'Ampere' is the unit of:
→ 67The unit 'Volt' is equivalent to:
→ 68An electric heater is rated 1500 W, 220 V. The current drawn by it is:
→ 69Two resistors of 10 Ohm and 20 Ohm are connected in parallel. The equivalent resistance is:
→ 70Two resistors of 10 Ohm and 20 Ohm are connected in series. The equivalent resistance is:
→ 71Resistivity of a conductor depends on:
→ 72The resistance of a conductor is inversely proportional to its:
→ 73How many electrons constitute one coulomb of charge?
→ 74What is the charge of an electron?
→ 75In an electric circuit, the conventional direction of current flow is:
→ 76A 220 V, 100 W bulb has a resistance of approximately:
→ 77Which of the following factors does not affect the resistance of a conductor?
→ 78When the cross-sectional area of a metallic wire is doubled, its resistance will:
→ 79When the length of a metallic wire is doubled, its resistance will:
→ 80If a wire of resistance R is cut into two equal halves, the resistance of each half will be:
→ 81Why are domestic electrical appliances usually connected in parallel?
→ 82The material used for the filament of an electric bulb is usually:
→ 83An electric fuse is used as a safety device in circuits to:
→ 841 kilowatt-hour is equivalent to:
→ 85The commercial unit of electrical energy is:
→ 86The SI unit of electric power is:
→ 87The rate at which electrical energy is consumed or dissipated in an electric circuit is called:
→ 88Which of the following is an application of the heating effect of electric current?
→ 89The heating effect of electric current is given by:
→ 90When resistors are connected in parallel, the reciprocal of the total resistance is equal to:
→ 91When resistors are connected in series, the total resistance is:
→ 92Which of the following materials has the lowest electrical resistivity?
→ 93The SI unit of electrical resistance is:
→ 94The resistance of a conductor depends on:
→ 95According to Ohm's Law, if the potential difference across a conductor is doubled, the current flowing through it will:
→ 96Ohm's Law states the relationship between:
→ 97A device used to measure potential difference across two points in an electric circuit is called:
→ 98The SI unit of potential difference is:
→ 99The work done in moving a unit charge from one point to another in an electric circuit is called:
→ 100A device used to measure electric current in a circuit is called:
→ 101The SI unit of electric current is:
→ 102The flow of electric charge is known as:
→ 103Which of the following is an example of an electrical insulator?
→ 104The SI unit of electric charge is:
→ 105What determines the rate at which energy is delivered by a current?
→ 106An electric iron of resistance 20 Ω takes a current of 5 A. Calculate the heat developed in 30 s.
→ 107Compute the heat generated while transferring 96000 coulomb of charge in one hour through a potential difference of 50 V
→ 108Why does the cord of an electric heater not glow while the heating element does?
→ 109What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series?
→ 110Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal?
→ 111Let the resistance of an electrical component remains constant while the potential difference across the two ends of the component decreases to half of its former value. What change will occur in the current through it?
→ 112Will current flow more easily through a thick wire or a thin wire of the same material, when connected to the same source? Why?
→ 113On what factors does the resistance of a conductor depend?
→ 114What is meant by saying that the potential difference between two points is 1 V?
→ 115Name a device that helps to maintain a potential difference across a conductor.
→ 116Calculate the number of electrons constituting one coulomb of charge.
→ 117Define the unit of current.
→ 118What does an electric circuit mean?
→ 119How much energy is given to each coulomb of charge passing through a 6 V battery?
→ 120What is the maximum resistance which can be made using five resistors each of 1/5 Ω ?
→ 121A current of 1 A is drawn by a filament of an electric bulb. Number of electrons passing through a cross section of the filament in 16 seconds would be roughly.
→ 122Calculate the resistivity of the material of a wire of length 1 m, radius 0.01 cm and resistance 20 ohms.
→ 123List the factors on which the resistance of a conductor in the shape of a wire depends.
→ 124Why are alloys commonly used in electrical heating devices ?
→ 125Calculate the resistance of a metal wire of length 2 meters and cross-sectional area 1.55 × 10⁻⁶ square meters, if the resistivity of the metal is 2.8 × 10⁻⁸ ohm meter.
→ 126How is the resistivity of alloys compared with those of pure metals from which they may have been formed?
→ 127Name a device that you can use to maintain a potential difference between the ends of a conductor. Explain the process by which this device does so.
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