[5 Marks Each] QUE-ANS

Question 15 Marks

Describe the following experiment with Diagram : To check whether the given material I object is a conductor or an insulator of electricity.

Answer

Given materials : Key, eraser, plastic scale, matchstick, glass bangle, iron nail, coin, rubber, pins, wooden block, pencil lead, thermocol, paper. Apparatus — Materials : Electric cell, torch bulb, three electric wires, insulating tape. Procedure:
$(1)$ Take an electric cell, a torch bulb and three wires.
$(2)$ Connect all the three as shown in Figure
$(a).$ Leave a small space in between the free ends of the wire.
$(3)$ Place the given objects in between the two free ends of the wire one by one.
$(4)$ In each case observe that the bulb glows or not? Note down your observations in Table Conductors and Insulators of electricity

Objects used in place of switch	Material it made of	Bulb glows? Yes/No
Key	Metal	Yes
Eraser	Rubber	No
Scale	Plastic	No
Matchstick	Wood	No
Glass bangle	Glass	No
**** nail	Metal	Yes

Conclusion:
$(1)$ Materials which allow electric current to pass through them are conductors of electricity (In the cases in which the bulb glows).
$(2)$ Materials which do not allow electric current to pass through them are called insulators (In the cases in which the bulb does not glow).

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Question 25 Marks

Describe the following experiment with Diagram : To construct an electric switch in an electric circuit.

Answer

Apparatus - Materials: Two drawing pins, a safety pin, two wires and a small sheet of thermocol.

Procedure: Procedure:
$(1)$ Take a safety pin and a drawing pin.
$(2)$ Insert a drawing pin into the ring at one end of the safety pin and fix it on the thermocol sheet.
$(3)$ Make sure that the safety pin can be rotated freely.
$(4)$ Now, fix the other drawing pin on the thermocol sheet in such a way that the free end of the safety pin can touch it. The safety pin fixed in this way would be your switch.
$(5)$ Now, make a circuit by connecting an electric cell and a bulb with this switch as shown in Figure $(b)$.
$(6)$ Rotate the safety pin so that its free end touches the other drawing pin. Observe the bulb.
$(7)$ Now, move the safety pin away. Does the bulb continue to glow? Observation and Understanding: When the safety pin touches both the drawing pins, it fills the gaps between them and completes the circuit. This condition is called ‘switch on’. When the free end of the safety pin is removed away from the drawing pm, the circuit becomes discontinuous arid the condition is known as ‘switch off’. Conclusion : A switch is used to turn on or turn off bulb or other electric equipments.

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Question 35 Marks

Describe the following experiment with Diagram : To connect a torch bulb and a cell using a wire. To complete and break the circuit. To understand the function of a switch by these activities.

Answer

Apparatus — Materials : An electric cell, torch bulb, wire, rubber band, electric tape.

Procedure:
$(1)$ Take a torch bulb, a cell and a piece of wire.
$(2)$ Remove the plastic covering at the two ends of the wire by the knife.
$(3)$ Wrap one end of a wire around the base of an electric bulb as shown in the figure.
$(4)$ Fix the other end of the wire to the negative terminal of an electric cell with a rubber band.
$(5)$ Now, bring the tip of the base of the bulb that is, its other terminal, in contact with the positive terminal of the cell. Does the bulb glow?
$(6)$ Now, move the bulb away from the terminal of the electric cell. Does the bulb remain lit? Observation:
$(1)$ As soon as the bulb is touched to the positive terminal of the battery, the circuit gets completed and the bulb glows.
$(2)$ When the bulb is removed from the positive terminal, the circuit breaks and the bulb stops glowing. Conclusion: The function of a switch : To complete the electric circuit and to close the electric circuit when needed.

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Question 45 Marks

Describe the following experiment with Diagram : To construct a simple circuit by using an electric cell and a torch bulb.

Answer

$(4)$ Fix the other exposed parts of the wires to the bulb. [See figure $(b)$.]
$(5)$ Connect the wires fixed to the bulb with those attached to the cell. [See figure $(C)$.]
$(6)$ Thus, the torch bulb glows.
$(7)$ The circuit thus made is a complete circuit.

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Question 55 Marks

Describe the following experiment with the diagram: To identify whether the given objects are electrical conductors or insulators.

Answer

Apparatus — Materials : Torch bulb, electric cell, insulating tape, pieces of conducting wire, rubber band, wood strip, pencil, key, pen refill, matchstick, safety pin, plastic spoon, aluminium wire, ebonite rod. Apparatus — Materials : Torch bulb, electric cell, insulating tape, pieces of conducting wire, rubber band, wood strip, pencil, key, pen refill, matchstick, safety pin, plastic spoon, aluminium wire, ebonite rod. Procedure:
$(1)$ Prepare an electric circuit as shown in the figure.
$(2)$ Keep enough distance between terminals $A$ and $B$ of the wire.
$(3)$ Connect the given materials between terminals $A$ and $B$ one by one.
$(4)$ Observe whether every time the bulb glows or not. Note down your observations in following table.

No.	Object	Does the ** glow? Yes No	Electrical Conductor/ Insulator
$1$	Rubber	No	Insulator
$2$	wooden strip	No	Insulator
$3$	Pencil	No	Insulator
$4$	Key	Yes	Conductor
$5$	Pen refill	No	Insulator
$6$	Matchstick	No	Insulator
$7$	Safety pin	Yes	Conductor
$8$	******* pin	No	Insulator
$9$	Aluminium wire	Yes	Conductor
$10$	Ebonite rod	No	Insulator

Conclusion:
$(1)$ Key, safety pin and aluminium wire are conductors of electricity.
$(2)$ Rubber band, wood strip, pencil, pen refill, matchstick, plastic spoon and ebonite rod are insulators.

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Question 65 Marks

Describe the following experiment with Diagram : To construct an electric switch in an electric circuit.

Answer

Apparatus - Materials: Two drawing pins, a safety pin, two wires and a small sheet of thermocol. Procedure:
$(1)$ Take a safety pin and a drawing pin.
$(2)$ Insert a drawing pin into the ring at one end of the safety pin and fix it on the thermocol sheet.
$(3)$ Make sure that the safety pin can be rotated freely.
$(4)$ Now, fix the other drawing pin on the thermocol sheet in such a way that the free end of the safety pin can touch it. The safety pin fixed in this way would be your switch.
$(5)$ Now, make a circuit by connecting an electric cell and a bulb with this switch as shown in Figure $(b)$.
$(6)$ Rotate the safety pin so that its free end touches the other drawing pin. Observe the bulb.
$(7)$ Now, move the safety pin away. Does the bulb continue to glow? Observation and Understanding: When the safety pin touches both the drawing pins, it fills the gaps between them and completes the circuit. This condition is called ‘switch on’. When the free end of the safety pin is removed away from the drawing pm, the circuit becomes discontinuous arid the condition is known as ‘switch off’. Conclusion : A switch is used to turn on or turn off bulb or other electric equipments.

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Question 75 Marks

Describe the following experiment with Diagram : To connect a torch bulb and a cell using a wire. To complete and break the circuit. To understand the function of a switch by these activities.

Answer

Apparatus — Materials : An electric cell, torch bulb, wire, rubber band, electric tape.
Procedure:
$(1)$ Take a torch bulb, a cell and a piece of wire.
$(2)$ Remove the plastic covering at the two ends of the wire by the knife.
$(3)$ Wrap one end of a wire around the base of an electric bulb as shown in the figure.
$(4)$ Fix the other end of the wire to the negative terminal of an electric cell with a rubber band.
$(5)$ Now, bring the tip of the base of the bulb that is, its other terminal, in contact with the positive terminal of the cell. Does the bulb glow?
$(6)$ Now, move the bulb away from the terminal of the electric cell. Does the bulb remain lit?
Observation:
$(1)$ As soon as the bulb is touched to the positive terminal of the battery, the circuit gets completed and the bulb glows.
$(2)$ When the bulb is removed from the positive terminal, the circuit breaks and the bulb stops glowing.
Conclusion: The function of a switch : To complete the electric circuit and to close the electric circuit when needed.

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Question 85 Marks

Describe the following experiment with Diagram : To construct a simple circuit by using an electric cell and a torch bulb.

Answer

Apparatus — Materials : An electric cell, a torch bulb, knife, electric tape, four electric wires. Procedure:
$(1)$ Take four electric wires with differently coloured plastic coverings.
$(2)$ Remove a little of the plastic covering from each length of the wire at the ends by the knife. This would expose the metal wires at the ends of each length.
$(3)$ Fix the exposed parts of the two wires to the cell. [See figure $(a)$.]
$(4)$ Fix the other exposed parts of the wires to the bulb. [See figure$(b)$.]
$(5)$ Connect the wires fixed to the bulb with those attached to the cell. [See figure $(C)$.]
$(6)$ Thus, the torch bulb glows.
$(7)$ The circuit thus made is a complete circuit.

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Science [5 Marks Each] QUE-ANS

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