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SCI - CLASS 10 (CBSE) > Chp-12 Electricity > Flashcards

Chp-12 Electricity Flashcards

1
Q

What is statics electricit and current electricity?

A

Static- deals with charges at rest

Current - deals with charges in motions

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2
Q

True or false- static electricity is most in insulator

A

True

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3
Q

What is frictional electricity.

A

The electricity developed on the surfaces of the insulating body when rubbed against each other is called frictional electricity

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4
Q

Define electric charge

A

Electric charge is the property associated with matter due to which it produces or experienced electric and magnetic effects

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5
Q

what is the study of electric charge at rest

A

Electristatics

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6
Q

which one gets + charged and which one - wh n rubbed against each other :-

1) Glass rod. Silk
2) Woolen cloth/ fur. Ebonite, amber, rubber
3) Woolen cloth. Plastic
4) Plastic comb and dry hair

A

positive +—> Glass rod, Woolen cloth,fur and dry hair

  • change —-> silk, ebonite,amber, plastic
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7
Q

What are some properties of electric charge

A

• There are two types of electric charge positive and negative. Like charges repel each other each other
• A total charge of the body is the algebraic some of all the individual contributions by various charges present on it each being taken with its proper sign. This property of charges call Additivity of charge
• Electric charge can neither be created nor destroyed
• Every charge is the integral multiples of a certain smallest amount of charge that exist in nature. This property of charge is called quantisation.
Q= +_ ne When N is equal to 1, 2 , three….And E is the elementary charge, the smallest charge that exist independently in nature
E= 1.6* 10-19

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8
Q

What is the unit of electric charge and define it in the terms of electric current

A

Electric charge is coulomb.
1 C is the defind as the amount of charge that flows through a given cross-section of a wire in one second if there is a steady current of 1 ampere flowing in the wire
Q=IT

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9
Q

What is coulombs law and derive it

A

The force of attraction repulsion between the two points at rest is directly proportional to the product of the charges and inversely proportional to the square of the distance between them and it always acts along the line joining the charges.
F= KQ1Q2
R^2
Where K is the constant of proportionality sometimes called the coulombs constant. For vacuum, K is equal to 9×10^9 Nm^2C^-2.

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10
Q

What is electric potential

A

Electric potential at a point a in an electric field is the work done per unit positive charge and transporting it from infinity far awayTo the point a.

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11
Q

True or false- Electric charge is a vector quantity.

A

False

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12
Q

T/F -

Electric potential is a scaler quantity

A

True

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13
Q

What is potential difference

A

Potential difference between the two points is defined as the work done in carrying a unit positive charge from one point to the other. V=W/Q

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14
Q

What is the SI unit of potential difference and define it in the term of potential difference

A

SI unit: volt
1 V is the potential difference between two points when one joule of work is done in moving a charge of 1C from one point to another

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15
Q

What are conductors and insulators. Give few examples

A

Conductors are the substances in which electricity can can flow quite freely. (Loosely bound electrons move when V is applied)
For example, metals: copper aluminium silver iron. Nonmetals: graphite. Electrolytic solutions: aqua solution of NaCl, sulphuric acid,HCL.

Insulators are the substances which do not allow the electric current to flow through them. For exampleRubber, glass, plastic, wood, porcelain, pure water, sugar,diamond

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16
Q

T/F If the work done in moving a unit positive charge from point a to point B is zero it means, potential of point and B are same

A

true- Va=Vb

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17
Q

Define electric current and its SI unit

A

Electric current is the rate of flow of electric charge through any cross-section. Its SI unit is called Ampere(named after Andre Marie- ampere) .

1A is the electric current flowing through a conducting wire when one C charge flows through it in one second
1A= c/S

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18
Q

T/F- Electric current in the scalar quantity

A

T

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19
Q

T/F— V between two points is dependent on the actual path followed between the pts

A

false, independent

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20
Q

What are current carriers

A

Current carriers are charged particles which flow in a particular direction to produce electric current. In solid conductors, current can use the free electrons. In liquid, current carriers are positive and negative irons. In gases positive ions and electrons are current carriers

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21
Q

What is the electromotive force

A

It is the max work done by a source of emf in taking a unit positive charge once around a closed circuit. The sources of emf maintain a potential diff between its terminals by doing work, which compel the electric current to flow in a particular direction in a closed circuit. Some sources of EMF are 1) Batttery or electrochemical cell 2)Generator 3) solar cells

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22
Q

T/F- Convention direction of electric current is the direction of flow of positive charge

A

True

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23
Q

How is the flow of Charge through a conductor dependent on. V

A

When there is no potential difference across a conductor directions of the Motion of free electrons present in it is randomly oriented such that there is no drift of electrons in a particular direction. Hence no current flows through it

When there is a potential difference applied across the conductor there is an average dript of electrons in a particular direction. Thus there is the net transfer of electrons across the conductor which results in electric current

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24
Q

_____device is connect in ____ and is used to measure the potential difference.____Is the device connected in _____to measure the electric current

A

Voltmeter ; parallel

Ammeter; series

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25
Q

Why is voltmeter connected in parallel

A

Voltmeter has a very high resistance, So it draws very little current from the circuit and hence has a very little affect on the voltage being measured

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26
Q

Why is connected amemeter in series

A

Amm etre has a very small resistance so it has a very little effect on current being measured. For an ideal ammeters resistance is zero

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27
Q

What is electric circuit

A

It is a continuous part which consists of various electric devices like blah, Tubelight, resistors each connected with each other through a conducting wire to the terminals of the source of EMF like battery is called electric circuit

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28
Q

What is circuit diagram

A

A diagram which indicates a different devices are connected inIn a circuit by proper electrical symbols for devices called circuit diagram

29
Q

What is electric resistance

A

Resistance is the property of a material which offers opposition to the electric current and dissipates energy. The ratio of applied potential difference to the resulting electric current inA close circuit is called electric resistance

30
Q

What is the SI unit of resistance. Define it

A

Ohm: When the potential difference of 1 V is applied across the ends of a conductor and the current produced in it is 1A are then the resistance of the conductor is 1 ohm

31
Q

State the ohms law given by George Simon Ohm

A

According to ohms law the current through the certain conductor is directly proportional to the potential differenceBetween its end at a constant temperature.

32
Q

T/F. Ohm’s law is an empirical law

A

T- It is not a fundamental law but a empirical law that holds approximately good for many substances particularly metals

33
Q

What is the resistor Name of few materials which are used for resistors

A

A physical device which has a principal characteristic of offering electrical resistance is called resistor.
Alloys like manganin, constantan and Nichrome are used in wire wound resistors.
Carbon resistors are used because they are compact and low-cost.
Copper and aluminium are generally used for transmission wires and connecting wires

34
Q

What does resistance depends on

A

Length of the conductor, cross-sectional area, type of material and temperature

35
Q

What is your resistivity

A

It is the characteristic property of a material and the resistance offered by a uniform conducting wire having unit length and unit area of cross-section. It depends on temperature and pressure

36
Q

When does the source of energy gets dissipated entirely in the form of heat

A

If an electric circuit is purely resistive, that is, it consist of resistors only connected to a battery, the source energy gets dissipated entirely in the form of heat. This effect is utilised inDevices such as geysers heater and iron

37
Q

What is the heating effect of current

A

The conversion of a part of the electric energy into heat energy when electric current flows through a device is called heating effect of currently

38
Q

Define power. And derive its formula

A 
Power is the rate at which heat/ energy is generated. And is defined as the work done per unit time by a source of EMF in order to maintain electric current in a circuit. It is the rate of doing work
P= H/t and W/t
—————————
W= VQ
P= W/T
= VQ/t 
= (Q/t)* V 
= VI
—————————-
P=VI
V^2/R (V= IR) 
—————————
P= VI
P= I^2* R (V= IR)
39
Q

What is the SI unit of electric power and define

A

SI unit: Watt= 1VA
1kilowatt = 1000Watt

If the electric current through a device is 1A are and a potential difference across it is 1 V, then its electrical power is 1WATT.

40
Q

What is electric energy. Give its formula and Si Unit

A 
The total energy supplied by a source of EMF in order to maintain electric current in a given time is called electric energy. 
E= p*t 
= VIT 
Si unit: Joules 
One Joule= 1VAs
If the energy is used at the rate of 1Watt, the total enrgy used in 1 sec is1 juole.
1 watt hour= 3600J
1 kilo watt hours=3.6* 10^6J
41
Q

State Joules lawof heating

A 
According to Jules law of heating, the heat produced in the resistor is directly proportional to the square of the current for a given resistance, directly proportional to the resistance in the Given current, and directly proportional to the time for which the current flows through the resistor
E= H= VIt 
 H= I^2 Rt (V= IR)
H=V^2 t 
        R

1cal= 4.186 J

42
Q

How is bulb an application of thermal effects of current

A

Electric bulb: The electric heating or Jules heating is used in producing light and electric bulb. Here the filament must retain as much of the heat generated as possible so that it gets very hot and emits light. To produce white light, the filament has to be heated to about 3000•C by passing current.It must not melt at such high temperature.thus an pelectric bulb consist of a filament of a strong metalWith a high melting point it is tungsten about 3380 (org- 3422°C)sealed in a glass bulb. the smaller enclosed volume makes it easier to maintain the required temperature, as without it the loss of heat will be more.The bulbs are usually filled with chemically inactive nitrogen or argon gases which prevent the oxidation of filament at high temperatures thereby increasing the life of bulbs.

43
Q

How is electric fuse and application of thermal effect of current

A

The safety device that doesn’t allow excessive current to flow through an electric current and used to prevent the electric appliances against electric current. It consist of a piece of wire made up of metal or an alloy of appropriate melting point fixed between two terminals of a fuse plug. for example aluminium, copper, iron, lead lead. Conducting wire made up of tin- 25% and lead: 75%. Having low melting point is used. The fuse wire is usually an enclosed porcelain or similar material with metal ends. It is put in series with an electric device in the circuit. If a current larger than the specified value of the current circuit, the temperature of the fuse wire increases and this meltd the fuse wire n breaking the circuit

44
Q

How does a source of EMF like cell create potential difference

A

Cells have chemicals inside. Reactions in the cells cause the positive and negative charges to gather separately. This creates a potential difference compelling current to move in a particular direction.

45
Q

T/F- Positive terminal has higher potential and negative lower potential

A

T

46
Q

T/F in a common dry cell, the small metallic cap at one end is negative and thr flat metallic plate is positive.

A

False; Metallic cap- positive

flat plate - negative

47
Q

T/F electrons move from higher potential to lower potential

A

F

48
Q

During experiments why should the plug key be closed only when required like when making measurements

A

bcoz this prevents cell from draining out quickly.when the cells is used for a long time, the potential difference drops to a smaller value

49
Q

How would you identify series and parallel connection

A

Two or more electric elements are said to be connected in series if the current flowing through one also flows through the rest

Two or more electric elements are said to be connected in parallel ur the same potential difference exist across them

50
Q

Verify ohms law

A

Ohm’s law : When the physical conditions such as temperature etc. remain same, the current flowing through the conductor is directly proportional to the potential difference applied across the ends of the conductor,
i.e., I ∝ V or V ∝ I ⇒ V/I = constant ⇒ V = IR Where R is constant of proportionality and is called resistance of the wire.
Necessary condition for validity of Ohm’s law is that physical condition such as temperature of the conductor remains same.
Procedure: Experiment to verify ohm’s law-
1) we take a conducor elts say, a nichrome wire and connect it to a key, source of EMF like battery, a voltmeter , an ammeter and rheostat.
2) we then close the key and the circuit completes. therefor current flows through the current and the voltage is applied
3) record the initial voltage and current shown by voltmeter and ammeter respectively
4) then gradually increase the current by sliding the rheostat.
5)now record the current flowing in the circuit and the corresponding value of potential difference across the resistance wire R
6)This way different sets of values of voltage and current are obtained by sliding rheostst.
7)For each set of values of V and I, the ratio of V/I is calculated.
When you calculate the ratio V/I for each case, you will come to notice that it is almost the same. So V/I = R, which is a constant.
Plot a graph of the current against the potential difference, it will be a straight line. This shows that the current is proportional to the potential difference.

51
Q

T/F For metals and alloys of metals, the resistivityincrease with increase in temperature

A

T

52
Q

How does the value of resistivity of metals makes them good conductor

A

Values of resistivity of metals are very small- of the order of 10^-8ohm m
This makes them a good conductor. Metals such as copper are therefor used for making electric wires.

53
Q

What is the values of resistivity of insulators

A

the values of resistivity of insulators such as glass and fused quartz are very high- of the order of 10^16 ohm m

54
Q

What makes alloys suitable for use in the heating element

A

Alloys like nichrome have 30-100 times larger values of resistivity than those of metals. Their resistance varies very little with temperature and these do not oxidise readily

55
Q

What are semi conductors

A

The materials in which the no of electrons is much greater than that in insulators and much smaller than that in conductors. Their resistivity decreases as the temperature increases. The resistivity of materials such as silicon and germanium are 10^5 - 10^10 more than that of metals, but 10^15. - 10^16 times less than that of insulators like fused quartz.

56
Q

Define equivalent resistance

A

The resistance of a single resistor that can replace a combination of resistors in any given circuit without any change in V across the terminals and current through the circuit is called equivalent resistance

57
Q

T/F the resistance of thin wire is less than that of thick wire

A

F

58
Q

T/F when a resistance is joined parallel to a comparatively smaller resistance, the equi resistance is very close to the value of smaller resistance

A

T

59
Q

Tell the formula of distribution of current in two resistors in parallel

A

i1= R2*I
R1+R2

i2 = R1*I
R1+R2

i1. = R2
i2 R1

60
Q

Define equivalent resistance

A

The resistance of a single resistor that can replace a combination of resistors in any given circuit without any change in V across the terminals and current through the circuit is called equivalent resistance

61
Q

Why do some devices have grills and fans?

A

Production of heat is inevitable. If the heat produced cannot be utilised, it represent wastage of energy. A considerable amount of energy is thus wasted in transmission of electricity from the generating station to our homes . Sometimes the heat produced in a device is so much that it can even damage the devise unless proper cooling arrangements are made. To dissipate heat in TV sets, monitors etc, their cabinets have grills to let air pass through them

62
Q

T/Fhigher the power rating, higher the resistance

A

F; high the power rating, smaller the resistance. so a 1000W heater has less resistance than 100w bulb

63
Q

How Does the (I) Thickness and (Ii) Length of a Fuse Wire Depend on Its Current Rating

A

the current rating of the fuse wire.

(i) Is directly proportional to the thickness of the fuse wire. Thicker the fuse wire, higher will be the current rating of the fuse wire.
(ii) The current rating of the fuse wire does not depend on its length.

64
Q

define current rating

A

The maximum current which fuse allows to pass through it is called current rating

65
Q

The voltage of the power generated at the generating stations is first stepped up before its transmission.Give reason

A

If the voltage is increased, the current decreases. Thus, the current loss can be reduced through the long range transmission line. Hence, the voltage is stepped up before transmission.

66
Q

why are fuse wire genearally thin?

A

If the fuse wires are thick, the larger cross section decreases the resistance across the fuse wire. So, even a high current flows through the fuse, it doesn’t blow out. Because it just acts as a normal electric contact in the circuit or wiring.In order to reduce the area and to maintain a minimum resistance to generate heat, fuses are made as thin.
A fuse wire should not have high resistance or low resistance. It should have enough resistance to carry its rated current without unwanted disconnection and melt instantly for a small excess of current. That is the fuse thickness increases with the current rating.

67
Q

what is meant by power rating pf an appliance?an bulb is rated 60w ,220V. what does this indicate?

A

The power rating of an electric appliance is the electrical energy consumed per second by the appliance when connected across the voltage of the mains. The values of power and voltage taken together form what is called power rating of an appliance.
A bulb having markings of 60 W, 220 V over it, indicates that the bulb will consume 60 J of energy per second when connected across the mains supply of voltage 220 V.

68
Q

what is short circuiting?

A

if the terminals of a device are joined by a connecting wire, i.e they are joined directly the, the device is said to short circuited. and the potential difference across it becomes zero.
A short circuit is to connect the positive and negative terminals of a battery together with a low-resistance conductor, like a wire. if the positive and negative terminals of a battery are joined by a connecting wire, i.e they are short circuited then large amount of current will flow trough it as resistance of the circuit becomes negligible.

69
Q

T/more heat is generated in series combination than parallel

A

power is more in parallel combination, therefore, heat is more generated in parallel combination as compared to series combination of resistances.
When two resistors are connected first in series and then parallel, the heat produced with parallel combination will be 4tines that with series combination

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