ELECTRIC CURRENT & ITS EFFECTS

**ELECTRIC CURRENT AND ITS EFFECTS**

1.      Define electric circuit?

Ans: Connection of electronic components, through which an electric current can flow.

2.      Draw symbols of fuse, variable resistor and galvanometer.

Ans: 

3.      How to connect voltmeter and ammeter in a circuit?

Ans: We need to connect voltmeter in parallel, across the electronic components and ammeter in series with electronic components.

4.      Draw a simple circuit with a bulb, switch and a resistor and also draw appropriate positions of voltmeter and ammeter to measure voltage across resistor and bulb.

5.      Payal connected a simple circuit with a cell, switch, resistor and bulb in series. She measured current through a bulb, resistor and she found that the ammeter reads same value. Why?

Ans: In series connection the current at every point is same, so if we connect ammeter at any point it will read the same value.

6.      Write the advantages of parallel connection over series connection.

Ans: In parallel connection, all the components get same amount of voltage, but in series connection, the voltage is divided according to their resistance value. If one component goes bad other will work, but in series connection if one goes bad others also will not work.

7.      Define open and closed circuit?

Ans: If the path of the electricity/current is broken or if the switch is open in any electric circuit, then the circuit is said to be an open circuit. If the path of electric current is not broken then the circuit is said to be closed circuit. Current will never flow in open circuit.

8.      What do you mean by a short circuit?

Ans:  If line(phase) or positive terminal and neutral wire get connected with each other, then a high current will flow through the wire this is  called short circuit.

9.      Write the applications of heating effect of electric current.

Ans: The heating effect of current is used in a large number of industrial and domestic appliances, such as

·         Immersion heaters

·         Hot plates, irons

·         Geysers

·         Electric kettles

·         Hair dryers.

10.  Write the applications of magnetic effect of electric current.

Ans:  Magnetic effect of electric current is used in Electromagnets

·         To remove iron splinters from our eyes/ body.

·         It is used in the cranes to lift heavy objects.

·         In loudspeakers

·         In telephone receiver and in the microphone.

·         In relays- to switch ON high power electric motors.

·         In electric motors, D.C. motors, electric fans they use electromagnet to convert electrical energy into mechanical energy.

11.  How wires get heated, when current flow through wires?

Ans: Every wire will have small resistance, when high current flows through these wires because this resistance heat is generated.

12.   Write the reasons for excessive current

Ans: A short circuit is the main reason for excessive current. Short circuit arises due to defect in the house wiring or insulation on wires, connection of many devices to a single socket may leads to overloading.

13.   The wires used for making electric circuit do not normally become hot. Why?

Ans: The wires which are used in circuit are good conductors, they have very low resistance (almost zero). So they will not get heated if current flow through them.

14.  In the below given diagram how can we control the brightness of the bulb? If we change the resistance from 0 to 100 Ω (ohms) write the voltmeter reading with resistance change.

Ans: In the above circuit variable resistor is connected in series with the bulb, so if we change the resistance of variable resistor the voltage across the bulb is also changes from 0-9V. So the brightness of the bulb changes with the resistance. The voltmeter across the bulb reads 0-9V.

15.   In the below given diagram

A.    Voltmeter 1 reading=?

B.     Voltmeter 2 reading=?

C.    Write the reading of both ammeters. What do you understood from these readings of ammeter?

Ans:  A. Voltmeter 1 reads 9V.

B. Voltmeter 2 reads 9V. (Because in parallel connection voltage across each component is same)

C. Both the ammeters reads same value i.e., 200mA. Because the in closed circuit is the current is same at any point. 

ALL THE BEST

some natural phenomenon_notes

Electric charge:

It is the property of matter that exhibits electrostatic repulsion or attraction.

Properties of charges

Like charges repel, unlike charges attract.

Types of charges

1. Positive charge: the example for positive charge is proton.

2. Negative charge: The example for negative is electron.

From where these charges will come

Atom consists of protons, which resides inside the nucleus, and electron which revolves around the nucleus in a particular orbit. Stable atom consist equal number of electrons and protons, so the net charge of a stable atom is zero.

When we remove electron from an atom the net charge becomes positive, and when atom gains electron the net charge become negative.

Methods to produce charge objects/ bodies:

1. charge by friction 2. Charge by Induction 3. Charge by conduction.

Charge by friction:

When two bodies rubbed each other the transfer of electrons takes place between two materials this process is known as charge by friction.

Charge by Induction

It is a method used to charge an object without actually touching the object to any other charged object.  

a charge is created by the influence of a charged object but not by contact with a charged object.  The word induction means to influence without contact.  

Take a metal sphere and keep it on an insulating stand.

The charged object (positively) is brought near the neutral metal sphere. Then the electrons are attracted by the charged object.

The electrons move to top of the metal sphere by leaving a positive charge, in this way positive charge and negative charges are separated in the metal sphere.

Now take a conducting wire and connect it to metal sphere and ground.  After grounding the metal sphere the electrons will flow to metal sphere and neutralize the positive charges which are at the bottom. The net charge on the metal sphere becomes negative.

Remove the conducting wire and also charged rod, now the negative charge appears on the total surface of the metal sphere.

Charge by Conduction:

Conduction just means that the two objects will come into actual physical contact with each other (this is why it is sometimes called “charging by contact”).

Overall the total negative charge remains constant.
● We started with six negative charges, and we ended up with a total of six negative.

● Notice that this also means a negative object causes a negative charge on the other object.

Question and Answers

1. Name the phenomenon that takes place when the heavy charge flows through air accompanied by heat and light?

Ans: lightning.

2. In what way lightning is useful?

Ans:  All living things depend on the chemical element nitrogen. Your body contains molecules known as proteins. Proteins are made up of several elements, including nitrogen. Nitrogen is essential for proteins but it is very hard to make into proteins. Even though 78 percent of our atmosphere is made of nitrogen, we do not get any nitrogen from the air we breathe. We simply inhale and exhale the nitrogen without using it.

When lightning slices through the atmosphere, it knocks electrons from the nitrogen atoms. The atoms are then free to combine with oxygen and hydrogen in the atmosphere forming nitrates. Rain carries this new compound to the earth enriching the soil with nitrates which are the building blocks of proteins. Plants synthesize these nitrates into proteins which can be used by animals and by us.

3. In what situations lightning can be dangerous?

Ans:  Open fields are more dangerous. Even though the park isn't the safest location either. When there is a thunderstorm, stay inside. In either a sturdy building or a car. More people are killed or injured by lightning, 62 percent of lightning deaths occur while people are participating in leisure activities.

4. List two uses of gold leaf electroscope?

Ans:Gold leaf electroscope is an instrument which is used

1. To detect whether the object is charged or not.
2. To detect type of charge on a charged body.
3. To detect  magnitude of electric charge.

5. What is lightning strike?  How we can protect ourselves from it?

A lightning strike is an electric discharge between the atmosphere and an earth-bound object. Find a shelter immediately stay indoors, doesn’t touch anything metal or electrical equipment, Cars and trains are safe because they are earthed.

6. List five safety measures against lightning strikes?

• Do not take shelter under a tree, an umbrella with a metallic end, in open garages, metal sheds or storage sheds.
• Do not lie on the ground.
• Do not sit near a window.
• A car, bus or building is a safe place to take shelter.
• If you are in a forest, take shelter under a small tree.

7. What do you find at the edges of the charged plates?

Ans: Charge always resides on the surface of the object. You would normally get more charge at the edges.

8. Explain why a charged balloon is repelled by another charged balloon where as an uncharged balloon is attracted by another charged balloon?

The nature of charges present on the surface of charged balloons are similar. Since like charges repel each other, two charged balloons repel each other. When a charged body is brought near an uncharged body, the uncharged body acquires charges on its surface caused by the induction of charges. The charges are of opposite nature in relation to the charged body. Since unlike charges attract each other, a charged body always attracts an uncharged body. Hence, an uncharged balloon is attracted by another charged balloon

When a charged balloon is placed near an un charged balloon, the charged balloon induces charges in uncharged balloon and attracts it.

9. How would you show that

A) like charges repel each other.

B) Unlike charges attract each other; describe the phenomenon with labelled diagram

Ans: Activity 15.3 (page num: 198

10. Describe with the help of a diagram an instrument which can be used to detect a charged body.

Ans: Gold leaf electroscope:

It consists of a metal rod. At one end of the rod, two leaves of gold foil are fixed and at the other end, there is a metal disc. The leaves of gold foil are placed inside a conical flask and the flask is corked to isolate the leaves from air. When the metal disc is touched with a charged body, the gold strips move away from each other. This happens because some of the charges of the body are transferred to the strips through the metal rod.

This method of charging a body is called charging by conduction. The nature of charges on both the leaves and the charged body are the similar. Hence, both the leaves of the gold foil will move away from each other. If the body was not charged, then the leaves of the foil would remain as they were before. They would not repel each other

12. The weather department has predicted that a thunderstorm is likely to occur on a certain day. Suppose you have to go out on the day. Would you carry an umbrella? Explain.

Ans: No, we should not carry umbrella. If thunderstorm occurs there is chance that lightning may strike the umbrella, has metal handle and is a good conductor of electricity you may get electric shock.  

13. Thunder is heard little latter than flash of lightning. Why?

Ans: Thunder means sound that produced because of sudden expansion of air. Light travels with high speed than sound.

14. A charged body loses its charge if we touch it with our hand. Why?

Ans: When we touch a charged body our body conducts its charges to the earth. That is why a charged body loses its charge, if we touch it with our hand. This phenomenon is known as electric discharge.

12. Value based question.

i. Because there is much probability that lightning may strike the tree rather than building.

ii. When thunder storm occurs we must take proper precautions.