Q1.State the factors on which strength of magnetic
field at a point due to a current
carrying conductor depends?
Ans. The factors on which strength of a magne tic field at a point depends.
(1) Amount of current (I) flowing through the conductor
(2) Distance (r) from the current carrying conductor.
Q2.What is an electromagnet? Write two uses of an e lectromagnet?
Ans.When current is passed through a solenoid it behaves as a magnet and is called as an electromagnet. The two uses of an electromagnet are-
(1) They are used to lift heavy iron pieces.
(2) They are used in many devices like micro phone, rad io sets, electric bell etc.
Q3.tate and define S.I unit of magnetic field?
Ans. The S.I unit of magnetic field is Tesla ( T). The magnetic field strength is said to be one Tesla if 1 meter long conductor carrying 1 ampe re current experiences 1 Newton force, when placed perpendicular to the dire ction of magnetic field.
Q4. current carrying conductor is placed perpendic ular to the uniform magnetic field. What happens to displacement of the conducto r if
(i) strength of current increases
(ii) If horse shoe magnet is replaced by a weak hor se shoe magnet.
Ans. The displacement of the conductor
(i) will increase on increasing the current
(ii) Will decrease on using a weak horse shoe magnet.
Q5.Define electromagnetic induction? Two circular coils A and B are placed close to each other. If the current in the coil A is changed , will some current be induced in the coil B? Explain.
Ans.Electromagnetic induction means the product ion of induced current in a closed coil due to the change in the magnetic field. When current in coil A is changed, magnetic flux sets up around coil A due to which some magnetic field set up in the coil B thus some induced current flow through coil B due to which galvanometer deflects.
Q6.Why does a current carrying conductor kept in a magnetic field experience force? What is the direction of force acting on the conductor?
Ans.A current carrying coil contains charged pa rticles which experiences a force (Bqv). The total force experienced by the charged particle is equal to the force experienced by the conductor which is perpendicular to both the magnetic field and the direction of current in the conductor.
Q7. (a) Distinguish between A.C and D.C?
(b) Which source produces alternating current?
Ans. Q8. (a) Define the term current rating of an electr ic fuse?
(b) Name the material used to make electric fuse?
(c) Name two safety measure commonly used in electr ic circuit and appliances?
Ans. (a) The maximum amount of current that can be passed through the fuse wire without melting it.
(b) Copper or alloy of lead acid tin
. (c) Electric fuses and earth wire.
Q9.Why do not two magnetic fie ld lines intersect each other?
Ans. The two magnetic field lines never intersec t each other because at the point of intersection there will be two directions of magnet ic field, which is not possible.
Q10,Name and state rule used to determine the direction of magnetic field produced around a straight conductor carrying current?
Ans. The rule is known as right hand thumb rule if a current carrying conductor is held in our right hand such that thumb points in the direction of current, then the curled fingers of the hand indicate the direction of magnetic field.
Q11.What is a soleno id? Draw magnetic field lines showing the magnetic field inside and outside the current carrying solenoid? Ans.A solenoid is a coil of many turns of insulated copper wire closely wound in the shape of a ring.
Q12.(a) Name f our appliances wherein an electric motor is used as an important component. In what respect it is different from gen erator?
(b) Define the terms used in the generator (i) armature (ii) slip rings (iii) brushes
Ans.The four appliances which have electric mot or inside them are (i) Mixers (ii) Washing machine (iii) Refrigerators (iv) Blenders
(i) Armature – Armature is a coil of large number of turns of insu lated copper wire wound over a soft iron core.
(ii) Slip rings- Slip Rings one two ring s made up of brass which rotates along with the coil.
(iii) Brushes- Brushes are made up of carb on which are pressed against the slip rings and are connected to external circuit where output is obtained.
Q13.(a) What is the standard colour code followed for (i) live (ii) neutral and (iii) earth wires used in electric ci rcuits?
(b) Which part of an electric appliance is earthed and why?
Ans.(a) The standard colour code for Live wire- Red Neutral- Black Earth- Green r espectively.
(b) The metallic case of an electrical appliance i s earthed because metals are good conductors of electricity and in case if curre nt exceeds i.e. live wire touches the metallic case of an appliance and then due to earthing all the excess amount of current flows down to the earth an d we prevent ourselves from an electric shock.
Q14.(a) What is short circuiting?
(b) What is overloading? How can you avoid overload ing?
Ans.a) Short circuiting means when live wire and the neutral wires come in contact with each other. Due to this resistance of the circ uit becomes very small and huge amount of current flows through the circuit wh ich is turn produces more heat which can cause fire.
(b) Overloading means large amount of current flows in the circuit. It can happen when many electrical appliances of high power ratin gs are connected in a single socket. It can be avoided by the following m ethods
(i) Not use too many appliance is a single socket
(ii) To apply preventive methods of short circuiting.
Q15.E xplain the principle, construction and working of a n electric motor with a help of labelled diagram?
Ans. Principle – it is based on the principal that a current carrying conductor placed perpendicular to the magnetic field experiences a f orce.
Construction- (1) Armature or coil- It consist of an insulated c opper wire wound on a soft iron core.
(2) Strong field magnet- two pole pieces of a stro ng magnet provides a strong magnetic field.
(3) Split ring- it consist of two halves 1 2 ( and R ) R of a metallic ring which reverses the direction of the current in a coil.
(4) Brushes- two carbon brushes touch the commutat or (split ring). (5) Battery – a battery is connected across the ca rbon brushes.
Q16.State two properties of magnetic lines of force?
Ans. (i) Magnetic lines of force are cl osed continuous curves.
(ii) The tangent at any point on the magnetic line of fo rce which gives the direction of magnetic field at that point.
Q17.Why does a compass needle deflected when brought ne ar a bar magnet ?
Ans. Compass needle experience a force is the magnetic field of a bar magnet due to which it deflects.
Q17.Write two ways to induce current in a coil?
Ans.) By moving a bar magnet toward or awa y from the coil.
(ii) By placing a coil near another coil connected across a battery.
Q18.What is the function of an earth wire? Why is if ne cessary to earth metallic casing of electric appliance?
Ans.Earth will acts as a safety device. Whe n live wire touches the metallic appliance then electric current flows through castling to the earth instead of human body and thus we prevent ourselves from getting shock. I t is necessary to earth metallic casing of the appliance because it saved e lectrical appliance from burning and prevent us from electric shock.
Q19.We know a current carrying conductor placed in a ma gnetic field experiences a force due to which the conductor moves. How do we t hink the rod displaces if- (a) current in rod is increased (b) a stronger horse shoe is inserted (c) length of the rod is increased.
Ans. Force acting on current carrying condu ctor F=BIL (a) When I increase, F also increases hence displacemen t of the rod increases.
(b) When a stronger horse shoe magnet is inserted, magn etic field B increases. So force F increase. Hence displacement increases.
(c) When I increases, force increases and hence displac ement increases.
Q20.
Ans. The factors on which strength of a magne tic field at a point depends.
(1) Amount of current (I) flowing through the conductor
(2) Distance (r) from the current carrying conductor.
Q2.What is an electromagnet? Write two uses of an e lectromagnet?
Ans.When current is passed through a solenoid it behaves as a magnet and is called as an electromagnet. The two uses of an electromagnet are-
(1) They are used to lift heavy iron pieces.
(2) They are used in many devices like micro phone, rad io sets, electric bell etc.
Q3.tate and define S.I unit of magnetic field?
Ans. The S.I unit of magnetic field is Tesla ( T). The magnetic field strength is said to be one Tesla if 1 meter long conductor carrying 1 ampe re current experiences 1 Newton force, when placed perpendicular to the dire ction of magnetic field.
Q4. current carrying conductor is placed perpendic ular to the uniform magnetic field. What happens to displacement of the conducto r if
(i) strength of current increases
(ii) If horse shoe magnet is replaced by a weak hor se shoe magnet.
Ans. The displacement of the conductor
(i) will increase on increasing the current
(ii) Will decrease on using a weak horse shoe magnet.
Q5.Define electromagnetic induction? Two circular coils A and B are placed close to each other. If the current in the coil A is changed , will some current be induced in the coil B? Explain.
Ans.Electromagnetic induction means the product ion of induced current in a closed coil due to the change in the magnetic field. When current in coil A is changed, magnetic flux sets up around coil A due to which some magnetic field set up in the coil B thus some induced current flow through coil B due to which galvanometer deflects.
Q6.Why does a current carrying conductor kept in a magnetic field experience force? What is the direction of force acting on the conductor?
Ans.A current carrying coil contains charged pa rticles which experiences a force (Bqv). The total force experienced by the charged particle is equal to the force experienced by the conductor which is perpendicular to both the magnetic field and the direction of current in the conductor.
Q7. (a) Distinguish between A.C and D.C?
(b) Which source produces alternating current?
Ans. Q8. (a) Define the term current rating of an electr ic fuse?
(b) Name the material used to make electric fuse?
(c) Name two safety measure commonly used in electr ic circuit and appliances?
Ans. (a) The maximum amount of current that can be passed through the fuse wire without melting it.
(b) Copper or alloy of lead acid tin
. (c) Electric fuses and earth wire.
Q9.Why do not two magnetic fie ld lines intersect each other?
Ans. The two magnetic field lines never intersec t each other because at the point of intersection there will be two directions of magnet ic field, which is not possible.
Q10,Name and state rule used to determine the direction of magnetic field produced around a straight conductor carrying current?
Ans. The rule is known as right hand thumb rule if a current carrying conductor is held in our right hand such that thumb points in the direction of current, then the curled fingers of the hand indicate the direction of magnetic field.
Q11.What is a soleno id? Draw magnetic field lines showing the magnetic field inside and outside the current carrying solenoid? Ans.A solenoid is a coil of many turns of insulated copper wire closely wound in the shape of a ring.
Q12.(a) Name f our appliances wherein an electric motor is used as an important component. In what respect it is different from gen erator?
(b) Define the terms used in the generator (i) armature (ii) slip rings (iii) brushes
Ans.The four appliances which have electric mot or inside them are (i) Mixers (ii) Washing machine (iii) Refrigerators (iv) Blenders
(i) Armature – Armature is a coil of large number of turns of insu lated copper wire wound over a soft iron core.
(ii) Slip rings- Slip Rings one two ring s made up of brass which rotates along with the coil.
(iii) Brushes- Brushes are made up of carb on which are pressed against the slip rings and are connected to external circuit where output is obtained.
Q13.(a) What is the standard colour code followed for (i) live (ii) neutral and (iii) earth wires used in electric ci rcuits?
(b) Which part of an electric appliance is earthed and why?
Ans.(a) The standard colour code for Live wire- Red Neutral- Black Earth- Green r espectively.
(b) The metallic case of an electrical appliance i s earthed because metals are good conductors of electricity and in case if curre nt exceeds i.e. live wire touches the metallic case of an appliance and then due to earthing all the excess amount of current flows down to the earth an d we prevent ourselves from an electric shock.
Q14.(a) What is short circuiting?
(b) What is overloading? How can you avoid overload ing?
Ans.a) Short circuiting means when live wire and the neutral wires come in contact with each other. Due to this resistance of the circ uit becomes very small and huge amount of current flows through the circuit wh ich is turn produces more heat which can cause fire.
(b) Overloading means large amount of current flows in the circuit. It can happen when many electrical appliances of high power ratin gs are connected in a single socket. It can be avoided by the following m ethods
(i) Not use too many appliance is a single socket
(ii) To apply preventive methods of short circuiting.
Q15.E xplain the principle, construction and working of a n electric motor with a help of labelled diagram?
Ans. Principle – it is based on the principal that a current carrying conductor placed perpendicular to the magnetic field experiences a f orce.
Construction- (1) Armature or coil- It consist of an insulated c opper wire wound on a soft iron core.
(2) Strong field magnet- two pole pieces of a stro ng magnet provides a strong magnetic field.
(3) Split ring- it consist of two halves 1 2 ( and R ) R of a metallic ring which reverses the direction of the current in a coil.
(4) Brushes- two carbon brushes touch the commutat or (split ring). (5) Battery – a battery is connected across the ca rbon brushes.
Q16.State two properties of magnetic lines of force?
Ans. (i) Magnetic lines of force are cl osed continuous curves.
(ii) The tangent at any point on the magnetic line of fo rce which gives the direction of magnetic field at that point.
Q17.Why does a compass needle deflected when brought ne ar a bar magnet ?
Ans. Compass needle experience a force is the magnetic field of a bar magnet due to which it deflects.
Q17.Write two ways to induce current in a coil?
Ans.) By moving a bar magnet toward or awa y from the coil.
(ii) By placing a coil near another coil connected across a battery.
Q18.What is the function of an earth wire? Why is if ne cessary to earth metallic casing of electric appliance?
Ans.Earth will acts as a safety device. Whe n live wire touches the metallic appliance then electric current flows through castling to the earth instead of human body and thus we prevent ourselves from getting shock. I t is necessary to earth metallic casing of the appliance because it saved e lectrical appliance from burning and prevent us from electric shock.
Q19.We know a current carrying conductor placed in a ma gnetic field experiences a force due to which the conductor moves. How do we t hink the rod displaces if- (a) current in rod is increased (b) a stronger horse shoe is inserted (c) length of the rod is increased.
Ans. Force acting on current carrying condu ctor F=BIL (a) When I increase, F also increases hence displacemen t of the rod increases.
(b) When a stronger horse shoe magnet is inserted, magn etic field B increases. So force F increase. Hence displacement increases.
(c) When I increases, force increases and hence displac ement increases.
Q20.
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