Multiple Choice Questions
- Which of the following terms does not represent electrical power in a circuit?
- An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the power consumed will be:
(a) 100 w
(b) 75 W
(c) 50 W
(d) 25 W.
- Two conducting wires of the same material and of equal lengths and equal diameters are first connected in series and then parallel in a circuit across the same potential difference. The ratio of heat produced in series and parallel combinations would be:
(d) 4: 1.
- A piece of wire of resistance R is cut into five equal parts. These parts are then connected in parallel. If the equivalent resistance of this combination is R’, then the ratio R/R’ is :
- Two charged bodies having equal potential are connected through a conducting wire, in this case :
(a) current will flow.
(b) current will not flow
(c) cannot say
(d) current will flow if a resistor is also connected.
- Which of the following correctly represents the relation among charge (Q), potential difference (V) and work done (W)?
(b) W = V/Q
(c) V = Q/W
(d) V = W/Q.
- An electric fuse is based on:
(a) the heating effect of the current
(b) the magnetic effect of the current
(c) the electrical effect of the current
(d) none of the above.
- A voltmeter is used to measure:
(a) potential difference
(b) electric current
(c) electric power
- The electrical energy dissipated in a resistor is given by :
(a) W = V/lt
(b) W = VI
(c) W = VI/t
- When two resistances of 6 22 and 12 22 are connected in parallel then the effective resistance is :
(a) 12 Ω
(c) 4 Ω
(b) 8 Ω
(d) 18 Ω
- S.I. unit of electric current is :
Ans. 1. (b), 2. (d), 3. (c), 4. (d), 5. (b), 6.(d), 7. (a), 8. (a), 9. (b). 10. (c), 11. (d).
Fill in the Blanks
- The unit of household consumption of electricity is…………..
- Two or more resistors are said to be connected in……….if came current flows through them.
- The resistance of a conductor is directly proportional to its…………..
- The effective resistance is less than any individual resistance when resistances are connected in …………
- When the cells of 1 V, 1-5 V and 2 V are connected in series, the resultant potential difference is……………
- Unit of specific resistance is…………
- If 90 coulomb charge passes through the conductor for 5 min, the current in the conductor is…………..
- Current is measured by an …………….
- The property of a material that resists electric current, is called…………
- Ammeter is connected in …………. in a circuit through which the current is to be measured.
- S.I. unit of electric potential is…………..
- S.I. Unit of electric currents is………………
Ans. 1. kilowatt hour (kWh), 2. series, 3. length, 4. parallel, 5. 4-5 V, 6. ohm – meter, 7. 0-3 A, 8. ammeter, 9. resistance, 10. series, 11. volt, 12. ampere.
Match the Columns
Column ‘A’ Column ‘B’
- Joule’s heating. (a) Watt
- Galvanometer (b) V = IR
- Ohm’s law (c) Ampere
- Power. (d) Fuse
- Electric current. (e) Direction of current
- Measurement of (f) Voltmeter
Ans. 1. (d), 2. (e), 3. (b), 4. (a), 5. (c), 6. → (f).
- A continuous and closed path of an electric current is called an electric circuit.
- Conventionally, in an electric circuit the direction of electric current is taken same as that of flow of electrons.
- I coulomb of charge is equal to charge contained in 6 × 10¹8 electrons.
- Charges flow in a copper wire by themselves.
- Rheostat is used to change resistance in the circuit.
- Metals and alloys have very low resistivity.
Ans. 1. True, 2. False, 3. True, 4. False, 5. True, 6. True.
Answer in one Word/Sentence
- What is the S. 1. unit of electric current ?
- What is a galvanometer?
Ans. An instrument used to detect presence and direction of current in a circuit is called galvanometer.
- On what factors, the resistance of a wire depends ?
Ans. Resistance of a wire depends on material, length and area of cross section of wire Ro I/A.
- What is the unit of power ?
- What is the commercial unit of electrical energy?
Ans. kilowatt hour (kWh).
- Write the unit of electric charge.
Very Short Answer Type Questions
- 1. Define the unit of current.
Ans. The unit of electric current is ampere (A). One ampere is defined as the flow of one coulomb of charge through a wire in one sec. Q.
- Name a device that helps to maintain a potential difference across a conductor.
Ans. Any source of electricity like battery, cell, power supply helps to maintain a potential difference across a conductor.
- 3. Define potential difference.
Ans. Potential Difference “The amount of work done in moving a unit positive charge from one point to another in an electric field is called the potential differencbetween those two point.” i.e…
- 4. What is meant by saying that the potential difference between two points is 1V?
Ans. If one joule of work is required to move a charge of one columb from one point to another, then it is said that the potential difference between the two points is 1 V.
- 5. What determines the rate at which the energy is delivered by a current
Ans. The rate of consumption of electric energy in an appliance is callled electric power. Hence, the rate at which energy is delivered by current is the power of the appliance. Q. 6. What do you understand by an electric circuit ? Ans. A continuous and closed path of an electric current is called an electric circuit An electric circuit consists of electric devices, source of electricity and wires that are connected with the help of a switch.
- 7. Calculate the number of electrons constituting one coulomb of charge.
Ans. One electron possesses a charge of 1-6x 10-19 Cie.. 1-6 × 10-19 C of charge
is contained in 1 electron.
: 1 C of charge is contained in 1/1-6 10-19 – 6-25 10¹8
Therefore, 6x 10¹8 electrons approximately constitute one coulomb of charge.
Q.-8. Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal?
Ans. The resistivity of an alloy is higher than a pure metal. Moreover, at high temperatures, the alloys do not melt readily. Hence, the coils of heating appliances such as electric toasters and electric irons are made of an alloy rather than a pure metal.
- 9. Why the cord of an electric heater not glow while the heating element does ?
Ans. The heating element of the heater is made up of an alloy which has very high resistance, so, when current flows through the heating element, it becomes too hot and glows red. But the resistance of cord which is made of copper or aluminium very low, so it does not glow.
- 10. Write the application of thermal (heating) effect of electricity.
Ans. Application of thermal effect of electricity-The thermal effect of electricity is utilised in the thermo-electric devices i.e., Electric irons, Electric heaters, geysers, etc. to produce heat and in electric bulbs to produce light. In fuse wires to protect the electrical appliances to be damaged.
- 11. How is voltmeter connected in a circuit to measure the potential difference between two points?
Ans. To measure the potential difference between two points, a voltmeter should be connected in parallel to the points.
- 12. Will current flow more easily through a thick wire or a thin wire of the same material, when connected to the same source? Why?
Ans. The current will flow more easily through a thick wire. It is because the resistance of a conductor is inversely proportional to its area of cross-section. The thicker wire, less is resistance and hence more easily the current flows.
Short Answer Type Questions
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