Chapter: Current Electricity – WBBSE Class 10 Physical Science
- How can we define electric current in a quantitative way?
Answer: In a quantitative way we can say that the rate of flow of electric charge through any cross section of a conductor per unit time is called the electric current. - What do you mean by D.C.?
Answer: If the electric current always flows in the same direction, then the current is called D.C. (Direct Current). - What do you mean by A.C.?
Answer: If the direction of current alternates, i.e., changes periodically from one direction to the opposite direction, then the current is called A.C. (Alternating Current). - What is electric cell?
Answer: A device in which electrical energy is obtained from the chemical energy is known as electric cell. - What is emf of a cell?
Answer: The potential difference between the electrodes of a cell in open circuit is called emf (electromotive force). - What is the direction of current in the external circuit of a cell?
Answer: Current flows from positive electrode to negative electrode in the external circuit of a cell. - What is the emf of a simple voltaic cell?
Answer: The emf of a simple voltaic cell is 1.08 volt. - What is the unit of charge in SI system?
Answer: The unit of charge in the SI system is coulomb. - What is the SI unit of current strength?
Answer: The SI unit of current strength is ampere. - What are the units of electromotive force and potential difference in SI system?
Answer: The SI unit of both electromotive force and potential difference is volt. - What is the SI unit of resistance?
Answer: The SI unit of resistance is Ohm. - 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. - How does the resistance of a conductor depend on the cross section of the conductor?
Answer: Resistance of the conductor decreases with increase of cross section. - What is 1 B.O.T.?
Answer: The total electric energy expended in 1 hour at the rate of 1 kilowatt is known as 1 B.O.T. (Board of Trade unit). - Which energy is converted to which other in an electric motor?
Answer: In an electric motor, electric energy is converted to mechanical energy. - What is earthing?
Answer: Earthing means connecting the metal case of an electrical appliance to the earth with the help of a metal wire. - Which effect of electric current is demonstrated in an electromagnet?
Answer: Magnetic effect. - How is current related to potential difference?
Answer: Current is directly proportional to potential difference. - What is the unit of resistivity in CGS system?
Answer: The unit of resistivity in CGS system is Ohm-cm. - 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. - What is voltmeter?
Answer: A voltmeter is used to measure the potential difference between two points in a section of an electrical circuit. - What is an ammeter?
Answer: An ammeter is used to measure the current flowing through an electric circuit. - What should be the resistance of an ideal ammeter?
Answer: Ideally, the resistance of an ammeter should be zero. - What should be the resistance of an ideal voltmeter?
Answer: Ideally, the resistance of a voltmeter should be infinity. - What are the metals used to prepare fuse wire?
Answer: Fuse wires are made from an alloy of lead (75%) and tin (25%). - What is the least value of electric charge available?
Answer: 1.6 × 10−19 C - Name two basic properties of electric charge.
Answer: (i) The electric charge of an isolated system is conserved.
(ii) Electric charge is quantised. - What is electric potential?
Answer: The electric potential at a point is the work done in bringing a unit positive charge from infinity to that point in the electric field. - Define electric potential difference between two points in an electric field.
Answer: It is the work done in bringing a unit positive charge from one point to the other point. - What is the direction of conventional current?
Answer: It is the direction opposite to the flow of electrons in a conductor under the influence of an electric field. - On what factors does the resistance of the conductor depend?
Answer: Resistance depends on:- Length (R ∝ l)
- Cross-sectional area (R ∝ 1/A)
- Material and temperature of the conductor
- What is the difference between Ohmic and Non-Ohmic conductors?
Answer: Ohmic conductors obey Ohm’s law while Non-Ohmic conductors do not obey Ohm’s law. - What do you mean by conductivity of a material? Give its SI unit.
Answer: It is the reciprocal of resistivity. Its SI unit is mho·m−1. - What is CFL?
Answer: CFL is Compact Fluorescent Lamp. - What is LED?
Answer: LED is Light Emitting Diode. - What is the value of permittivity of vacuum?
Answer: ε0 = 8.854 × 10−12 C2 N−1 m−2 - What do you mean by EMF of a cell?
Answer: EMF is the energy spent per unit charge in taking one unit positive charge around the complete circuit. - What do you mean by internal resistance of a cell?
Answer: It is the resistance offered by a cell to the flow of current within it. - Is Joule heating a reversible effect?
Answer: No, it is irreversible. Reversing the current does not reverse the heating effect. - When an electric bulb is connected to a 12 V battery, it draws a current of 1A. What is the power of the bulb?
Answer: P = V × I = 12 V × 1 A = 12 W - Which rule is known as Motor rule?
Answer: Fleming’s Left Hand Rule. - What type of energy transfer takes place in a dynamo?
Answer: A dynamo converts mechanical energy into electrical energy. - What is the definition of ohm?
Answer: 1 Ohm is the resistance when 1 ampere current flows due to 1 volt potential difference. - State Ohm’s law.
Answer: At constant temperature, the current through a conductor is directly proportional to the potential difference across its ends. - Definition of resistance from Ohm’s law?
Answer: Resistance is the ratio of potential difference to the current flowing. - Specific resistance of copper at 20°C is 1.6 × 10−6 ohm-cm. What does it mean?
Answer: It means resistance across 1 cm3 cube of copper at 20°C is 1.6 × 10−6 ohm. - What is watt-hour? Whose unit is it?
Answer: Watt-hour is the energy consumed by a 1 W appliance in 1 hour. It is a unit of electrical energy.
1 watt-hour = 3600 joules - Define 1 kilowatt-hour.
Answer: Energy consumed by a 1000 W appliance in 1 hour. It is also known as 1 Board of Trade (BOT) unit. - Why is nichrome wire used in electrically heated appliances?
Answer: It has high resistance, produces large heat, and doesn’t oxidize when red-hot. - What is short circuiting and what is overloading?
Answer:- Short circuiting: Direct connection between terminals causing excessive current flow.
- Overloading: Excessive current due to multiple appliances drawing current simultaneously.
- What is Oersted’s experiment?
Answer: A current-carrying wire deflects a magnetic needle placed nearby, showing magnetic effect of current. - State Ampere’s swimming rule.
Answer: A man swimming in current direction sees the north pole deflecting to his left. - State Fleming’s Left Hand Rule.
Answer: First finger = magnetic field, second finger = current, thumb = force (motion). - A bulb is marked ‘230 V-60 W’. What does it indicate?
Answer: At 230 V, the bulb consumes 60 joules of electrical energy per second. - What is a solenoid?
Answer: A coil formed by winding insulated wire in many turns around a cylinder; core used in electromagnets. - State Joule’s laws of heating effect of current.
Answer:- Heat ∝ I2 (for constant R, t)
- Heat ∝ R (for constant I, t)
- Heat ∝ t (for constant I, R)
Thus, H = 0.24 × I2RT (in calories)
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