Worksheet Solutions: Magnetic Effects of Current

# Magnetic Effects of Current Class 10 Worksheet Science

Objective Type Questions
Q1: The strength of an electromagnet after the limit cannot be increased by increasing the current through the solenoid. What is the reason behind this phenomenon?
(a) Electrons start to corrode the solenoid.
(b) Voltage through the solenoid gradually starts to decrease.
(c) Resistance of the solenoid increases.
(d) Current flowing through the solenoid is saturated.
Ans:
D
The strength of an electromagnet is determined by the amount of current flowing through the solenoid. However, there is a limit to how much current the solenoid can carry. Once this limit is reached, the current is said to be saturated. Thus, increasing the current beyond this point will not increase the strength of the electromagnet.

Q2: A proton enters a magnetic field at right angle to it, as shown below. The direction of force acting on the proton will be:
(a) To the right
(b) To the left
(c) Out of the page

(d) Into the page
Ans:
D
According to Fleming's left-hand rule, when a proton enters a magnetic field at a right angle, the force will act in a direction that is perpendicular to both the velocity of the proton and the magnetic field. In this case, the force will act into the page.

Q3: The magnetic field strength of a solenoid can be increased by inserting:
(a) a wooden piece into it.
(b) an iron piece into it.
(c) a glass piece into it.
(d) paper roll into it.
Ans:
B
The magnetic field strength of a solenoid can be increased by inserting a material that can be magnetized, such as iron. Iron is a ferromagnetic material, which enhances the magnetic field within the solenoid.

Q4: Rashita and her friends were decorating the class bulletin board.
She accidently dropped the box of stainless steel pins by mistake. She tried to collect the pins using a magnet. She could not succeed. Why?
(a) They are not using the magnet in right direction
(b) Steel pins are very heavy and cannot be lifted magnet
(c) Steel pins are very long
(d) Steel is not magnetic in nature
Ans:
D
Stainless steel is not magnetic in nature. Therefore, Rashita could not pick up the pins using a magnet. Stainless steel is an alloy of iron, chromium, and other elements. The presence of chromium makes it resistant to rust and also non-magnetic.

Q5: Which of the following correctly describes the magnetic field near a long straight wire ?
(a) The field consists of straight lines perpendicular to the wire.
(b) The field consists of straight lines parallel to the wire.
(b) The field consists of radial lines originating from the wire.
(d) The field consists of concentric circles centred on the wire.
Ans:
D
The magnetic field around a long straight wire is in the form of concentric circles centred on the wire. This is because the magnetic field lines emerge from the North pole and enter the South pole, forming a closed loop.

Q6: Which of the following combination is not correct?
(a) Electric Motor—Fleming's right hand rule
(b) Electric generator—Electromagnetic induction
(c) Earth wire—Green colour
(d) Compass Needle—Small Magnet
Ans:
A

The combination of an electric motor and Fleming's right hand rule is not correct. An electric motor works on the principle of Fleming's left-hand rule, which is used to find the direction of force in a current-carrying conductor placed in a magnetic field.

Q7: If the current is passing through a straight conductor. then, the magnetic field lines around it forms a particular shape. That shape is:
(a) Straight lines
(b) Concentric circles
(c) Concentric ellipse
(d) Concentric parabolas
Ans:
B
The magnetic field lines around a straight current-carrying conductor form concentric circles. This is because the magnetic field lines emerge from the North pole and enter the South pole, forming a closed loop.

Q8: A 3 pin mains plug is fitted to the cable for a 1 kW electric kettle to be used on a 250 V a.c. supply which of the following statements is not correct?
(a) The fuse should be filled in the live wire.
(b) A 13 A fuse is the most appropriate value to use.
(c) The neutral wire is coloured black.
(d) The green wire should be connected to the earth pin.
Ans:
B
The statement that a 13 A fuse is the most appropriate value to use for a 1 kW electric kettle on a 250 V a.c. supply is not correct. The current I = P/V = 1000/250 = 4 A, so a 4 A fuse should be used, not a 13 A fuse.

Q9: In the given electric circuit, the device X is:
(a) Ammeter
(b) Resistance
(c) Galvanometer
(d) Voltmeter
Ans:
C
In the given electric circuit, the device X is a galvanometer. A galvanometer is a sensitive instrument used to detect and measure small electric currents.

Q10: The strength of magnetic field inside a long current carrying straight solenoid is:
(a) more at the ends than at the centre.
(b) minimum in the middle.
(c) uniform at all points.
(d) found to increase from one end to the other.
Ans:
C
The strength of the magnetic field inside a long current carrying straight solenoid is uniform at all points. This is because the solenoid is long and the magnetic field lines are parallel and equidistant from each other inside the solenoid.

Q11: Why does a current-carrying conductor experience a force when it is placed in a magnetic field?
Ans: A current-carrying conductor produces a magnetic field around it. This magnetic field interacts with the externally applied magnetic field and as a result the conductor experiences a force.

Q12: What is the shape of a current-carrying conductor whose magnetic field pattern resembles that of a bar magnet ?
Ans:
A solenoid

Q13: How is the strength of the magnetic field at a point near a wire related to the strength of the electric current flowing in the wire ?
Ans:
Strength of magnetic field is directly proportional to the strength of current flowing in the wire.

Q14: Define magnetism.
Ans:
The property by virtue of which a magnet attracts certain metals such as iron, cobalt, nickel etc., is termed as magnetism.

Q15: Define electromagnetic induction.
Ans:
The production of electricity from magnetism is called electromagnetic induction.

Q16: A stationary charge is placed in a magnetic field. Will it experience a force ? Give reason to justify your answer.
Ans:
No, a magnetic field exerts a force only on a moving charge.

Q17: What happens to the magnetic field lines due to a current carrying conductor when the current is reversed ?
Ans:
The direction of magnetic field (and magnetic field lines) gets reversed on changing the direction of flow of current in a straight conductor.

Q18: Name five main parts of a D.C. motor.
Ans: An electric motor is a device which converts the electrical energy into mechanical energy.
The five main parts of a D.C. motor are:
(a) Strong field magnet,
(b) Armature coil,
(c) Split ring or commutator,
(d) Carbon brushes, and
(e) Battery.

Q19: Where will be the value of magnetic field maximum due to current-carrying circular conductor?
Ans:
At the centre of current-carrying circular loop.

Q20: State the conclusion that can be drawn from the observation that a current-carrying wire deflects a magnetic needle placed near it.
Ans:
A magnetic field is produced around a current-carrying conductor.

Q21: (a) What is the function of an earth wire in electrical instruments? Why is it necessary to earth the metallic electric appliances?
(c) What is the usual capacity of the fuse wire in the line to feed:
(i) lights and fans?
(ii) appliances of 2 kW or more power?
Ans: (a) We can get an electric shock on touching a faulty appliance, caused by the leakage of current from the appliance. Earthing provides a safety measure against the electric shock caused by the leakage of current. Earth wire brings this leakage current to the ground by a earth wire and we remains safe.
(b) Short circuiting takes place when a live wire and neutral wire come in contact with each other due to damage of insulation of these wires. Due to short circuiting, resistance of the circuit becomes minimum and a very high current is passed through the circuit which produces spark and heat and may lead a fire in the house. Overloading when the amount of current flowing through the circuit exceeds the rating of the protective devices it is said that circuit is overloaded. It is a situation in which many electrical appliances are connected in a single socket. It will draw more current, may lead the burst of fire in building.
(c) (i) Bulbs, fans etc. – 5A, (ii) Heater – Micro-oven, Electric iron – 15A

Q22: (a) State Fleming’s left hand rule.
(b) Write the principle of working of an electric motor.
(c) Explain the function of the following parts of an electric motor.
(i) Armature (ii) Brushes (iii) Split ring
Ans: (a) Fleming’s left hand rule state that if the thumb, forefinger and middle finger are stretched perpendicular to each other in such a way that forefinger indicates the direction of magnetic field, middle finger indicate the direction of current in the conductor then thumb will indicate the direction of force on the conductor.

(b) The principle of electric motor is that when a current carrying coil is placed in a magnetic field it experiences a torque and if the coil is allowed it rotates in the magnetic field.

(c) Function of the parts of an electric motor :

• Armature: Armature is a large number of turns of the coil on soft iron core which rotates in magnetic field.
• Brushes: They allow current to pass from external source to armature.
• Split rings: Split rings are of copper, splits into two halves and make a connection between armature and brushes.

Q23: (a) Explain what is the difference between direct current and alternating current? Write one important advantage of using alternating current.
(b) An air conditioner of 2 kW is used in an electric circuit having a fuse of 10 A rating. If the potential difference of the supply is 220 V, will the fuse be able to withstand, when the air conditioner is switched on? Justify your answer.
Ans:
(a) Direct current is a unidirectional current with constant magnitude. Alternating current is a current which change its magnitude and direction after a fixed period. AC voltage can be increased or decreased. Where is dc voltage cannot be increased or decreased. AC can be transmitted to long distances with lesser power loss.

(b) Given P = 2 kW and V = 200 volt,
Power, P = VI ⇒ I = P/V
I = 2000/220 = 9.09 A
The rating of the fuse wire is 10 A which is greater than current drawn by air conditioner so when air conditioner is switched on, fuse will not blow off.

Q24: (a) State the function of ‘a fuse’ in an electric circuit. How is it connected in the domestic circuit?
(b) An electric fuse of rating 3A is connected in a circuit in which an electric iron of power 1.5 kilo watt is connected which operates at 220 V. What would happen? Explain.
Ans:
(a) Fuse is a safety device to prevent the damage of electrical devices from short circuit or overloading. A fuse is connected in series with the circuit.
(b) Given Power P = 1.5 kW = 1500 Watt and V = 220 Volts.
Power P = VI ⇒ I = P/V = 1500/220 = 6.8 A
The rating of fuse is 3A which is lesser the current drawn by electric iron 6.8 A. So fuse wire will be blown.

Q25: (a) Explain any three properties of magnetic field lines.
(b) Give two uses of magnetic compass.
Ans
: (a) Properties of magnetic field lines:

• Magnetic field lines emerge from N pole and merge at S pole outside a bar magnet and travel from S pole to N pole inside the magnet.
• These are continuous and closed curves.
• Two field lines never intersect each other

(b) Uses of magnetic compass :

• In navigation it is used to find direction.
• It is used to detect the magnetic field.
• It can be used to test whether a substance is magnetic or not.

Q26: Explain the meanings of the words “electromagnetic” and “induction” in the term electromagnetic induction. List three factors on which the value of induced current produced in a circuit depends. Name and state the rule used to determine the direction of induced current. State one practical application of this phenomenon in everyday life.
Ans: The word electromagnetic means that an electric potential dipole is being produced in a coil due to change in magnetic field. The word induction means that the current has been induced. The value of induced current produced in a circuit depends on the following factors:

• number of turns in given coil
• area of each turn in coil
• rate of change of magnetic field.

The rule is Fleming’s right hand rule. Stretch the thumb, forefinger and middle finger of righthand perpendicular to each other that forefinger indicates the direction of magnetic field, thumb gives the direction of motion (or force) of the conductor, then middle finger will point the direction of induced current.
Application: AC generator or DC generator.

Q27: (a) An electric current is passed in a horizontal copper wire from east to west. Explain your observations  when a compass needle is placed (i) below this wire, (ii) above the wire. Draw inference from your observations.
(b) List the factors on which the strength of the magnetic field due to a straight conductor carrying current depend. How should these be changed to decrease magnetic field at a point?
Ans: (a) The direction of deflection of a magnetic compass needle depends upon the direction of the magnetic field at that point. The direction of the magnetic field due to a current carrying wire is given by the right hand screw rule. The direction of magnetic field below and above the wire is opposite so deflection in compass needle changes as well i.e, the deflection is reverse direction.
(b) The factors affecting strength of the magnetic field due to a straight wire carrying current:

• magnitude of current in the wire ∝ I
• distance of the point from the wire ∝ 1/I

By decreasing current or increasing the distance of the point from the wire, strength of magnetic field also decreases.

Q28: (a) Name two electrical appliances of daily use in which electric motor is used.
(b) Name and state the principle on which an electric motor works.
Ans:
(a) Drill machine, fan, grinder
(b) An electric motor works on the Fleming’s left hand rule. When a current carrying coil is placed in a magnetic field it experience a torque due to which it rotates.
Fleming’s left hand rule-stretch left hand, thumb, forefinger and middle finger perpendicular to each other in such a way that forefinger indicates the direction of magnetic field, middle finger indicates the direction of current in the conductor then thumb will point the direction of force on the conductor,

Q29: (a) What is an electromagnet? What does it consist of?
(b) Name one material in each case which is used to make a : (i) permanent magnet (ii) temporary magnet.
(c) Describe an activity to show how you can make an electromagnet in your school laboratory.
Ans:
a. A soft metal core made into a magnet by the passage of electric current through a coil surrounding it. It consists a soft iron core or its alloy and a solenoid conductor coil around the core.
b. (i) To make a permanent magnet alloy Alnico is used. (ii) Soft iron is used to make temporary magnet.
c. Take a long nail and put it into a solenoid of insulated copper wire. Pass the strong current in the solenoid the nail inside the solenoid becomes magnetised. This is called electromagnet.

Q30: (a) A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is:
(i) pushed into the coil with its north pole entering first?
(ii) withdrawn from inside the coil?
(iii) held stationary inside the coil?
(b) Name the above phenomenon and mention the name of the scientist who discovered it. State the law that relates the direction of current in the coil with the direction of motion of the magnet.
Ans: a. (i) Galvanometer gives a deflection
(ii) Again galvanometer gives a deflection but in opposite direction.
(iii) No current is induced in the coil so no deflection in the galvanometer.
b. Electromagnetic induction (EMI):
Faraday discovered it. Fleming’s right hand rule gives the direction of induced current in the coil. If we stretch right hand thumb, forefinger and middle finger perpendicular to each other in such a way that thumb gives the direction of motion of the conductor, forefinger gives the direction of magnetic field then middle finger will give the direction of current induced in the conductor.

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