SCERT KERALA TEXTBOOKS SOLUTIONS & STUDY NOTES: Class 9 Physics (English Medium) Chapter 06 Current Electricity
SCERT Solutions for Class 9 Physics Chapter wise
Physics Questions and Answers in Malayalam
Class 9 Study Notes Physics - Chapter 6: Current Electricity
Current Electricity- Study Notes, Textual Questions and Answers & Model Questions
* It is the movement of charges that creates current. In conductors, the current is formed by the flow of free electrons. But in electrolytes and gases, it is formed due to the flow of ions.
In order to have a flow of electrons through a conductor, there should be a potential difference between its ends. The current flows from the point of high potential to the point of low potential. The unit of potential
difference is ‘volt’. A voltmeter is used to measure a potential difference. The current sources like generator, dynamo or cell maintain potential difference and produce current in a circuit.
The ability of a current source to maintain the potential difference between the ends of a conductor is electromotive force (emf). The unit of emf is also 'volt'. Combinations of cells.
* Combinations of cells.
The combination of the cells is called a battery. Cells can be combined in two different modes.
1. Series connection.
This mode of connection is employed to make available large current in a circuit at high voltage. When the cells are connected in series the current through each cell will be equal.
2. Parallel Connection.
cells. The total emf available from this mode of connection is the same as that of a single cell.
The intensity of Current (I): Current or Intensity of current is the quantity
of charge that flows through a conductor in a circuit in one second.
Current, I = Q/t
Current is a scalar quantity. Its unit is coulomb/second. It is called ampere (A). Ammeter is used to measure current. It should be connected in series in the circuit.
Ohm's Law: It is the law that relates current through a conductor and potential difference between its ends.
When the temperature remains constant, the current through a conductor is directly proportional to the potential difference between its ends.
That is, V/I = constant(R)
This constant is the resistance of the conductor.
The unit of resistance is volt/ampere. It is called 'ohm' and is denoted by Ω.
When the potential difference between the ends of a conductor is 1 V and if a current of 1 A flows through it, then the resistance of the conductor is 1Ω.
The resistance of a conductor (resistor) depends on the nature of the substance, length and thickness of the conductor.
That is, Resistance R = ρL/A
Here L – length of the conductor, A – cross-sectional area of the conductor and ρ – the resistivity of the material. At a particular temperature, each substance will have a definite resistivity.
The resistance of a conductor increases with length and decreases with an increase in the area of cross-section.
The resistance of a conductor of unit length and unit area of cross-section is the resistivity of the material. Its unit is ohm metre (Ωm).
Rheostat: Rheostat is a device used to regulate the current in a circuit by changing the resistance gradually. the resistance of a uniform wire will be proportional to its length. This principle is made use of in a Rheostat. The picture and symbol of rheostat are shown below.
PRACTICE QUESTIONS & ANSWERS
1. Fill in the blanks.
a. The flow of electrons is responsible for current in conductors. But in electrolytes, it is due to the flow of ......
b. There should be a temperature for flowing heat from one object to another. For current flowing through a conductor, there should be ..... between the ends of the conductor.
Answer:
a. ions.
b. potential difference.
2. It is by including the source of emf, the current is made possible in it.
a.Give a few examples of a source of EMF.
b. What is the unit of emf?
Answer:
a. cells, dynamo, generator.
b. volt.
3. For proper working, each component in a circuit are to be connected properly.
b. Draw a circuit that consists of all of them.
Answer.
a. cell b: lamp c: ammeter. d. voltmeter e. switch.
4. There are three cells of ems 1.5V and a lamp in the circuit.
a. How are the cells connected in the circuit?
b. What is the voltage likely to be available for the lamp?
c. Suppose 3A current flows through the lamp now. If one of the
cells is removed from the circuit what will be the current then?
Answer:
a. in parallel.
b. 1.5V (When cells are connected in parallel, the effective voltage will
be same as that of a single cell)
c. 3A (When cells are connected in parallel, current will be the same as that from a single cell whatever be the number of cells in the combination)
5. a. Revi has 4 cells having emf 1.5 V each. Which mode of connection is to be employed for getting 6V emf from the cells? (parallel/series)
b. If a 12Ω resistor is connected to this circuit, what will be current?
c. Name the law used to calculate the current.
Answer:
a. series.
b. I = V/R = 6/12 = 0.5A
c. Ohms law.
6. Current in a circuit is 2A.
a. Name the device used to measure current.
b. Calculate the charge flowing through this circuit in each second.
Answer:
a. Ammeter.
b. We have Electric current is the rate of flow of charge. Since the current in the circuit is 2A, 2C charge will flow in each second.
7. 2C charge is flowing through a conductor in 10 seconds. Calculate current.
Answer: I = Q/t = 2/10 = 0.2A
8. The current through a conductor will be proportional to a potential difference between its ends.
a. What is called this law?
b. What is known as the proportional constant of potential difference and current?
Answer:
a. Ohms law.
b. Resistance of the conductor.
9. Complete the second pair according to the first pair.
a. C/s: ampere; V/A: …..
b. electric charge: coulomb; potential difference: ……
c. Electric current:ammeter ; potential difference: …….
Answer:
a. ohm b. volt c. volt meter.
10. It is given the potential difference between the ends of a conductor and the corresponding current in the table.
b. What is the resistance of the conductor?
c. Give the symbol of a resistor.
Answer:
a. 
b. R = V/I = 12/1 = 12 Ω
c. 
11. A B and C are iron wires of different size. The thickness of A&B are the same but the length is different. And the length of A & C are equal but the thickness is different.
a. Of the wires A and B, which will have high resistance?
b. From the first two circuits, find the lamp which likely to glow with more brightness? Why?
c. From circuits 1&3, identify the lamp having more brightness. Justify the answer.
Answer:
a. Since A is longer than that of B, the resistance of A will be greater.
b. Current will be higher in the circuit.2, because its resistance is small. Hence the lamp in circuit. 2 will glow with more brightness.
c. Since the wire in circuit.3 is thicker than that in A, resistance in circuit.3 will be less than that of circuit.1. Therefore brightness will be more in the circuit.3.
12. Q is the midpoint of the resistor AB.
If 4A current flowed through the resistor when the switch was turned on as shown in the figure, then
a)If point S touches the midpoint Q of AB, what will be the current in the circuit?
b)In the same circuit, if point A is connected to point B and S touches the midpoint Q of AB, then what will change the current?
c)If the conductor AB is stretched and doubled in length, will the current in the circuit be changed?
d) Explain your answer
Answer:
a) When V / I = R; V / R = I
when S touches the midpoint Q, R is reduced by half, V / R / 2 = I; V / R = 2I The electric current doubles I = 8A
b) The length in half and the area of cross-section is twice I = 4A
when length becomes half R = R / 2 The area of the cross-section is twice
R = R / 2 * 2: I = 16A
c) The length is doubled and the area of the cross-section is half
R = R * 2 * 2 = 4R: I = 1A
13. Length and thickness of a conductor are two factors influencing its resistance. Write down two more factors that influence the resistance of a conductor.
Answer: nature of the substance and temperature.
14. Identify the relation in the first pair and complete the second pair Current is formed in conductors; By the flow of free electrons
Current is formed in electrolytes and gases; ...................................
Answer:
By the flow of ions.
15. Which among the following doesn’t influence the resistance of a conductors
(length, Area of cross-section, density, resistivity)
Answer: Density
16. A table related to the resistance of a conductor is given. Complete the table
a- 20ohm
b-5 ohm
c-10 ohm
d- 20 ohm
17. Resistance of a conductor depends on its temperature. What is the relation between resistance and temperature of a conductor?
Answer: Resistance increases with temperature.
18. a. Identify the device shown in the figure.
c. What is the use of this device?
Answer:
a. Rheostat.
b. 
c. It is used to regulate the current in a circuit by changing the resistance.
19. Resistivity is the resistance of a conductor of unit length and unit area of cross-section.
a. What is the unit of resistivity?
b. If a uniform wire is cut into half, what will be the change in its resistance?
c. What happens to its resistivity?
Answer:
a. ohm metre. (Ωm)
b. Resistance will be halved.
c. There is no change in its resistivity.
20. The instrument used to regulate the current in a circuit by gradually changing the resistance is ------
Answer: Rheostat
21. XY is a uniform nichrome wire of high resistance.
b. The end J is made to contact at P first and then at Y. When
does the lamp glow with more brightness? Justify your answer.
Answer:
a. ohm (Ω)
b. Brightness will be greater when it touches at P. Because when it touches at P, only half of the resistance wire includes in the circuit and hence resistance in the circuit will be small.
22. AB is a metal wire. What will happen to the brightness of the lamp, if the wire is getting heated? Why?
When it is heated, its resistance will be increased and hence the brightness of the lamp will decrease.
23. "In parallel connection of cells, current will not be changed even if
the number of cells is increased"
a. Is the statement true?
b. If yes what is the use of this type of arrangement?
Answer:
a. The statement is true.
b. When we need a large current for a longer time, a parallel combination of a sufficient number of cells is more convenient.
24. The resistance of a bulb is 42Ω. The current passed through the conductor when 230 V supplied is given in the table. Complete the table
a)
Answer:
a) R=522.7Ω
b) No. When temperature increases the resistance also increases.
25. Find out the relation from the first pair and complete the second pair
kgm/s² : N
Volt/ Ampere : .............
Answer: Ohm
26. A current is flowing through a soldering iron having resistance 500Ω. Find out the voltage between the ends of the soldering iron.
Answer:
According to Ohms law,V = IxR
= 500x0.2= 100v
27. 10A current is flowing through a heater working in 230V. Calculate the resistance of the heating coil.
Answer:
According to Ohms Law V/I=R
=230/10=23Ω
28. The 20-coulomb charge passed in 5 seconds through a circuit when connected to a 12-volt battery.
a) What is the intensity of current through the circuit?
b) Which instrument is used to measure the Intensity of current?
c)Draw a circuit by including this device.
Answer:
a) 4A
b) Ammeter
c) 
29. Find the relation from the first pair and complete the second pair
Potential difference: Voltmeter
Intensity of current: ...............................
Answer: Ammeter
30. Find the relation from the first pair and complete the second pair
Potential difference: Volt (V)
Intensity of current: ...................
Answer: Ampere
31. Calculate the intensity of current if a charge of 40 coulomb passes through a circuit in 8 seconds.
Answer: I =Q/t
I =40/8= 5A
32. Some symbols are given in column A. Find out the suitable names from column B for each one and write against it.
a. cell b- Resistance, c-Bulb, d- Switch, e- Rheostat
33. a. Identify the component marked as X in the circuit.
Answer:
a. Resistor.
b.
34. Identify the following device/tools related to electric current or circuit. And Write down their use.
a. Multimeter: For measuring voltage, current and resistance. It is also used to check whether a circuit is
open or closed.
(b): Electric tester: It is used to check the presence of current. And it can also be used as a screwdriver.
(c): Soldering Iron: It is used to solder the ends of wires and electronic components in a circuit.
(d). Clamp Ammeter: It is used to measure current in a circuit without connecting wires or devices in the circuit.
35. a. Calculate the current in the circuit.
Answer:
a. Current, I = V/R = 6/3 = 2A
b. When the temperature remains constant, the current through a conductor is directly proportional to the potential difference between its ends.
36. In the circuit, AB is a nichrome wire and the current in the circuit is 2A.
b. If the wire AB is stretched to double its length,
i. what will be the resistance then?
ii. what will be current?
Answer:
a. Resistance R = V/I = 6/2 = 3 Ω
b.i. When it is stretched, its length will be doubled and thickness will be halved. Therefore the resistance will be increased to four times.
So the new resistance = 4x3 = 12 Ω
ii.Current, I = V/R = 6/12 = ½ A
37. There are two Dry cells and a resistor in the circuit. Emf of the cell is 1.5V.
b. What will be the voltage available across the resistor?
c. Calculate the current in the circuit.
Answer:
a. in series.
b. V = 1.5 +1.5 = 3V
c. Current, I = V/R = 3/1.5 = 2A
38. Observe the circuit diagram given below and answer the questions.
b) How will you connect an ammeter in the circuit to measure the current?
Answer:
a) parallel
b) series
39. Cells connected in two different ways are shown below.
b) what change will happen to the effective voltage in the two arrangements?
Answer:
a) series, b) parallel
b) voltage increases in series
Voltage doesn’t change in parallel connection
40. identify the relation from the first pair and complete the second pair
Generator; Mechanical energy---- Electrical energy
Cell: ............................ ..........................
Answer:
Chemical energy -----> electrical energy
41. Which among the following are not a source of emf.
(Generator, Electric heater, solar cell, electrochemical cell, Electric motor)
Answer:
Electric heater, Electric motor.
42. if 10J work is done while moving 1 coloumb charge from P to Q , what is the potential between the points
Answer: 10V
Physics Textbook (pdf) - Click here
PSC Solved Question Papers ---> Click here
PSC EXAM PROGRAMME -> Click here
CURRENT AFFAIRS QUESTIONS -> Click here
PSC Degree Level Questions & Answers - Click here
PSC LDC/LGS Questions & Answers - Click here
PSC RANK LISTS / SHORTLISTS -> Click here
 Chapter 06 CURRENT ELECTRICITY .){kind=link}
0 Comments