16 May 2011

Electric Current & and Its Effect CBSE PHYSICS Question Banks






CBSE PHYSICS Question Banks 10th Electric Current and Its Effect
(Q.1) A man has five resistors each of value 0.2 ohms. The maximum resistance he can obtain by connecting them will be (1 mark )
(a) 0.1 ohm
(b) 1.0 ohm
(c) 0.04 ohm
(d) 0.4 ohm

(Q.2) In a circuit the current flowing through a resistor is 1 Ohm per second. The heat generated in the 4 ohm resistor is ( 1 mark )
(a) 2 cal/s
(b) 3 cal/s
(c) 4 cal/s
(d) 10cal/s

(Q.3) What is electric current? ( 1 mark )

(Q.4) What is the SI unit of electric current? ( 1 mark )

(Q.5) What is the SI unit of electric charge? ( 1 mark )

(Q.6) Which metal is the best conductor of electricity at room temperature? ( 1 mark )

(Q.7) Why are metals able to conduct electricity? ( 1 mark )

(Q.8) How should the resistances be connected so that the equivalent resistance is increased? ( 1 mark )

(Q.9) The length of the wire is doubled, what is the change in its resistively? ( 1 mark )

(Q.10) Why is tungsten used as filament in bulbs? ( 1 mark )

(Q.11) There is change in the length of the wire, will its resistance change?( 1 mark )

(Q.12) How is power related to current and voltage? ( 1 mark )

(Q.13) Range of resistively of metals and alloys is: ( 1 mark )
(a) 10-7 to 10-5 m
(b) 10-6 to 10-4 m
(c) 10-7 to 10-4 m
(d) 10-8 to 10-6 m

(Q.14) Direction of conventional current is from ( 1 mark )
(a) Negative terminal to positive terminal
(b) Positive terminal to negative terminal
(c) In any direction
(d) In both the directions

(Q.15) Electric current is defined as the ( 1 mark )
(a) Rate of flow of charges (b) Total quantity of charges flowing through the circuit.
(c) Number of electrons flowing through the circuit.
(d) Number of ions flowing

(Q.16) S.I. Unit of current is ( 1 mark )
(a) Ampere
(b) Coulomb
(c) Volt
(d) Watt

(Q.17) Potential difference is defined as ( 1 mark )
(a) The amount of work done in moving a unit charge in a unit time
(b) Distance between two terminals
(c) Length of the connecting wire
(d) The amount of work done in moving a unit charge from one point to another.

(Q.18) S.I. Unit of potential difference is ( 1 mark )
(a) Volt
(b) Coulomb
(c) Ampere
(d) Watt

(Q.19) 1 microampere is equivalent to ( 1 mark )
(a) 6.25 x 109 electrons
(b) 6.25 x 106 electrons
(c) 6.25 x 1012 electrons
(d) 6.25 electrons

(Q.20) The length of a wire is doubled, but its cross section remains the same, then its resistance will become ( 1 mark )
(a) 4 times
(b) 2 times
(c) ½ times
(d) 8 times

(Q.21) Resistance of a conductor do not depends upon ( 1 mark )
(a) The length of the conductor
(b) Area of cross section of the conductor
(c) Material of the conductor
(d) Temperature of the conductor

(Q.22) According to Ohm’s law ( 1 mark )
(a) Current is directly proportional to the potential difference
(b) Current is inversely proportional to the potential difference
(c) Current is equal to the potential difference
(d) Current is independent of potential difference

(Q.23) Heat produced due to flow of current through a conductor is given by the formula ( 1 mark )
(a) H = I2 R t
(b) H = V I/ t
(c) H = V t / R
(d) H= It

(Q.24) 1volt= ( 1 mark )
(a) 1joule/1newton
(b) 1joule/1cm
(c) 1joule/1coulomb
(d) 1newton/1metre

(Q.25) The combined resistance of any number of resistances connected in series is equal to ( 1 mark )
(a) The sum of individual resistances
(b) The sum of reciprocals of individual resistances
(c) Product of individual resistances
(d) Highest individual resistance

(Q.26) The reciprocal of the combined resistance of any number of resistances connected in parallel is equal to ( 1 mark )
(a) The sum of reciprocals of individual resistances
(b) Reciprocal of the product of individual resistances
(c) Reciprocal of sum of all the resistances
(d) Sum of individual resistances

(Q.27) When two or more resistors are connected in series ( 1 mark )
(a) The current passing through each resistor is same
(b) The potential difference across each resistor is same
(c) Current is inversely proportional to the potential difference
(d) Potential difference and current are independent

(Q.28) When two or more resistors are connected in parallel ( 1 mark )
(a) The current passing through each resistor is same
(b) The potential difference across each resistor is same
(c) Current and potential are inversely proportional
(d) Current increases linearly

(Q.29) Commercial unit of electrical energy is ( 1 mark )
(a) Joule
(b) Coulomb
(c) Watt
(d) k W h

(Q.30) The work done in moving a charge of 3 C across two points having potential difference 20V ( 1 mark )
(a) 40J
(b) 60J
(c) 80J
(d) 100J

(Q.31) Power rating of an electric appliance indicates ( 1 mark )
(a) The rate of consumption of electrical energy.
(b) Amount of heat evolved.
(c) Brightness of the light.
(d) Quality of the appliance.

(Q.32) One kilowatt hour = ( 1 mark )
(a) 3.6 x 106 J
(b) 3.6 kJ
(c) 1000 watt
(d) 3.6 x 106 calories

(Q.33) What happens to the heating effect when the direction of current is reversed? ( 1 mark )
(a) Cooling effect is observed
(b) Amount of heat remains unchanged
(c) There will be a short circuit
(d) Current will increase suddenly

(Q.34) Alloys are usually used in electrical heating devices because ( 1 mark )
(a) Resistively of an alloy is generally higher than that of constituent elements.
(b) Alloys oxidize readily at high temperature.
(c) Alloys are bad conductor of heat
(d) Alloys do not have free electrons

(Q.35) An electric bulb of 40 W is connected to a source of 220 V, the current drawn by the bulb will be ( 1 mark )
(a) 0.18 A
(b) 18 A
(c) 1.8 A
(d) 180 A

(Q.36) Electrical energy consumed in lighting an electrical bulb of 60 W for 5 hours is ( 1 mark )
(a) 3 kWh
(b) 1.08 x 106 J
(c) 5KWh
(d) 2.03 x 106 J

(Q.37) What is the melting point of tungsten? ( 1 mark )
(a) 30500C
(b) 35780C
(c) 33800C
(d) 38500C

(Q.38) Difference of electric pressure is called: ( 1 mark )
(a) Electric difference
(b) Potential difference
(c) Charge difference
(d) Volt difference

(Q.39) An electric iron consumes energy at a rate of 840W when it is connected to a source of voltage 220V. The current flowing is ( 1 mark )
(a) 3.81A
(b) 3A
(c) 2A
(d) 1.4A

(Q.40) What is the minimum resistance that can be obtained using three 5 ohm resistors? ( 1 mark )
(a) 5 ohm
(b) 1.6 ohm
(c) 15 ohm
(d) 1 ohm

(Q.41) A refrigerator rated 400W operates 8hour per day. The total number of commercial units for 30days will be ( 1 mark )
(a) 96
(b) 46
(d) 100

(Q.42) What is ohm’s law? Give its mathematical expression? ( 2 Marks )

(Q.43) How much current will an electric heater coil draw from a 220 volt line, if the resistance of the heater coil is 40 ?( 2 Marks )

(Q.44) Calculate the number of electrons constituting one coulomb of charge. ( 2 Marks )

(Q.45) The combination of resistances shown below has equivalent resistance equal to 12 ohm, what is the value of R?(2Marks )

(Q.46) Calculate the amount of charge that would flow in 1 hour through the elements of an electric bulb drawing a current of 0.4 A. ( 2 Marks )

(Q.47) What is the power of an electric lamp, if it draws 20 A current when connected to 220 V line? ( 2 Marks )


(Q.48) The potential difference between the terminals of an electric heater is 30 volt when it draws current of 4 A from the source. What current will the heater draw if the potential difference is increased to 120 volt? ( 3 Marks )
(Q.49) A current of 4 A exists in a 10 resistor for 4 minute. Find the charge and the number of electrons that pass through any cross-section of the resistor in this time. ( 3 Marks )

(Q.50) A 100 watt electric bulb is lighted for 2 hours daily and four 40 watt bulbs are lighted for 4 hours daily. Calculate the electric energy consumed in kwh in 30 days. ( 3 Marks )


(Q.51) Two lamps, one rated 100 W at 220 volts and the other 60W at 220 volts are connected in parallel to a 220 V supply. What current is drawn from the supply line? ( 3 Marks )


(Q.52) To produce 1000 joule of heat in 10 seconds, how much voltage should be applied to 50 resistance. ( 3 Marks )


(Q.53) In the circuit diagram given below, find the equivalent resistances and total current flowing through the circuit.(3Marks )


(Q.54) a) State the law, which relates the current in a conductor to the potential difference across its ends.
b) Draw the V-I graphs for a
(i) Metallic conductor.
(ii) Liquid Electrolyte.
(iii) Vacuum tube.
c) A simple electric circuit has 24 V batteries and a resistor of 30 ohm. What will be the current in the circuit? ( 5 Marks )


                                 Electric Current and Its Effect
Q. 1. Why is Tungsten metal selected for making filaments of incandescent lamp bulbs?
Q. 2. A torch bulb is rated at 3V and 600mA. Calculate it’s
a) Power b) Resistance c) Energy consumed if it is lighted for 4 Hrs.
Q. 3. Why pure iron is not used in making permanent magnets. Name materials used for making permanent magnets. Describe how permanent magnets are made electrically? State two examples of electrical appliances which use permanent magnets.
Q. 4. Which will offer more resistance a 50W lamp or 25W lamp bulb and how many times?
Q. 5. What are magnetic field lines? How is the direction of a magnetic field lines at a point determined?
Q. 6. Draw two field lines around a bar magnet along its length on its two sides and mark the field direction on these by arrows.
Q. 7. List any three properties of Magnetic lines of force.
Q. 8. Should the heating element of an electric iron be made of iron, silver or nichrome wire? Why.
Q. 9. A steady current is passed for 30minutes through two voltmeters connected in series: a copper voltmeter [Cu cathode in copper sulphate solution], and a silver voltmeter [Ag cathode in silver nitrate solution]. If the mass of copper deposited in the first voltammeter is 21.17g, Calculate the mass of silver deposited on the cathode in the other voltammeter. Given relative atomic mass of Cu = 63.5 and Ag = 108.
Q. 10. State Fleming’s left hand rule. With a labeled diagram, describe the working of an electric motor. What is the function of a Split ring commutated in a motor?
Q. 12. What is the principle behind the working of an A/C generator? How can we find the direction of the current in the armature of the generator?
Q. 13. If a wire is stretched to triple its original length, what happens to its resistively?
Q. 17. State the rule to find the direction of magnetic field produced around a current carrying conductor. State the characteristics of magnetic force.
Q. 18. Give differences between magnetic and electric force.
Q. 19. Two identical resistors each of resistance 10 ohm are connected 1) in series 2) in parallel, in line to a battery of 6volts. Calculate the ratio of power consumed in the combination of resistors in the two cases.
Q. 20. What are the factors on which the strength of magnetic field produced by a current carrying solenoid depends?
Q. 21. A bulb is rated at 220V- 100W. What is its resistance? Five such bulbs burn for 4 hrs. What is the energy consumed? Calculate the cost if the rate is 50paise per unit?
Q. 22. Express ohm’s law mathematically. Draw a circuit diagram to verify Ohm’s law. Present the relationship between the voltage applied across a conductor and the current flowing through it graphically.
Q. 23. State Right hand thumb rule for finding the direction of magnetic field, around a current carrying straight conductor. How will the magnetic field be affected :
a. On increasing the current
b. On changing the direction of flow of current.
Q. 24. What type of energy transformations take place in electric motor? Name two devices which use electric motor as necessary component?
Q. 25. Two lamps rated 100W, 220V and 25W, 220V are connected in parallel to 220V supply. Calculate the total current through the circuit.
Q. 26. A metallic coil connected to a 220V supply has a resistance of 110 ohm. How long will it take this coil to heat 1kg water from 2o0C to 700C? Assume whole heat produced by coil is taken up by water. (Specific heat capacity of water = 4186 )
Q. 27. Why is much less heat generated in long electric than in filaments of electric bulb?
Q. 29. Should the heating element of an electric iron be made up of iron, silver or nichrome wire?
Q. 30. For longer operational life why dry cells should be used intermittently?
Q. 33. How does the resistance of wire change when 1) Its length is doubled 2) Area is doubled?
Q. 35. An electric kettle rated 1000W, 220V is used to bring water at 20 degrees to its boiling point. If the kettle is switched on for 10 minutes. Calculate:
a. The resistance of the element of kettle
b. Current flowing through the element
c. Mass of water in the kettle.
Q. 37. A copper wire has a diameter of 0.5mm and resistively of . How much of this wire is required to make a 10 ohm coil?
Q. 38. A wire of resistance 5ohm is bent in the form of a closed circle. What is the effective resistance between the two points at the end of any diameter of the circle?
Q. 40. State Fleming’s Left and right hand rules. With a labeled diagram describe the working of an electric motor. What is the function of commutate rings in a motor?
Q. 41. What is the effect on resistively of a pure metal with the increase in temperature?
Q. 42. What is a fuse? How does it function? Explain the terms: Short Circuiting, Overloading and Van Allen belts.
Q. 43. How are ammeter and voltmeter connected in circuit? What are the ideal resistances for these components?

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