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Goyal Brothers Electricity and Magnetism-1 Class-9 ICSE Physics Ch-10

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Unit I Exercise 1

Practice Problems

Unit II Exercise 2  Objective Questions

Unit II Exercise 2  Subjective Questions

Unit I Exercise 1

Goyal Brothers Electricity and Magnetism-1 Class-9 ICSE Physics Ch-10

Question 1.
There is a positively charged sphere A and negatively charged sphere B, such that they are brought in electrical contact by a copper wire. Answer the following questions :

(a) Which sphere is at higher potential before electrical contact on the basis of convention?
(b) Which sphere is at lower potential before electrical contact on the basis of convention?
(c) In which direction conventional current flows?
(d) In which direction electronic current flows?
(e) What is potential of the spheres after electrical contact?

Sphere A is positively charged and sphere B is negatively charged.
Both the sphere A and B are brought in electrical contact by a copper wire.

(a) On the basis of convention, positively charged sphere A is at higher potential before electrical contact.
(b) On the basis of convention, negatively charged sphere B is lower potential before electrical contact.
(c) Conventional current flows from sphere A to sphere B i. e. from a body at higher potential to the body at lower potential.
(d) Electronic current flower from sphere B to sphere A i.e. from a body at lower potential to the body at higher potential.
(e) After electrical contact, both the spheres will be at same potential.

Question 2.

(a) What do you understand by the term electric potential?
(b) Define electric potential in terms of energy spent.
(c) State the unit of electric potential and define it.

(a) Electric potential : The amount of work done in moving a unit positive charge from infinity to a given point in an electric field is called electric potential.
(b) Electric potential : The amount of energy spent in moving a unit positive charge from infinity to a given point in an electric field is called electric potential.
(c) Volt is the SI unit of electric potential.
One volt : When one coulomb of charge is brought from infinity to a given point in an electric field, such that work done is one joule, then electric potential is said to be one volt.
OR
Electric potential is said to be one volt if one Joule of work is done in moving one coulomb of charge from infinity to a given point in an electric field.

Question 3.

(a) What do you understand by the term quantity of electric charge?
(b) State SI unit of electric charge and define it.
(c) How many electrons constitute one unit electric charge in SI system?

(a) Quantity of electric charge : The number of charge (electrons) which drift from lower to higher potential is called quantity of charge.
(b) SI unit of electric charge is coulomb (C).
One coulomb : The quantity of electric charge which will deposit 0.00118 g of silver on the cathode, when passed through silver nitrate is called one coulomb.
(c) 6.25 × 1018 electrons constitute one unit (IC) electric charge in SI system.

Question 4.

(a) What do you understand by the term electric current?
(b) State and define the SI unit of electric current.
(c) State the relation between electric current; number of electrons moving in a circuit and time in seconds.

(a) Electric current : The rate of flow of electric charge in an electric circuit is called electric current.
(b) Ampere (A) is the SI unit of electric current.
One ampere : When one coulomb charge flows through an electric circuit in one second, then the electric current flowing the circuit is said to be ampere.
(c) If Q is the charge (in coulombs) flowing through conductor in time t (in seconds) such that current I flows through the conductor then
Rate of flow of charge = Q/t
We know rate of flow of charge = I = Electric current.
⇒ I = Q/t

Question 5.
How electric current flows in (i) solids, (ii) liquids?
(i) Flow of electric current in solids : In solids, the positive charges are associated with atomic nuclei. As the nuclei are firmly packed and closely held by inter-atomic forces, therefore, positive charges cannot drift.
On the other hand, negative charges (electrons) are not held firmly. Thus, when a potential difference, however small, is applied they start drifting from lower to higher potential.
The continuous drift of electrons, through the body of a solid conductor constitutes the current.
(ii) Flow of electric current in liquids : Within a liquid no electrons move. However, when a negatively charged and a positively charged electrodes are placed in a liquid, it sets up an electric field.
Under the influence of the electric field, the positively charged ions migrate towards the negatively charged electrode and vice versa.
At the cathode the positively charged ions gain electrons. At the anode the negatively charged ions lose same number of electrons.
Thus, in a way number of electrons given by the cathode is equal to the number of electrons accepted by the anode. The sum up, we can say that simultaneous movement and discharge of positive and negative ions in the opposite directions constitutes the current in the liquids.

Question 6.

(a) Define the term potential difference.
(b) How is potential difference related to work done and quantity of charge?

(a) Potential difference : The amount of work done in moving a unit positive charge from one point to another point in an electric field is called potential difference.
(b) If Q = Charge moving from one point to another in an electric field.
W = Work done to move the charge Q from one point to another.
V = Potential difference between two points.
Then work done in moving Q units of charge = W
Work done in moving one unit of charge = W/Q
But work done in moving one unit of charge = Potential difference = V
⇒ V = W/Q

Practice Problems

Goyal Brothers Electricity and Magnetism-1 Class-9 ICSE Physics Ch-10

Practice Problems 1

Question 1.
A charge of 5000 C flows through an electric circuit in 2 hours and 30 minutes. Calculate the magnitude of current in circuit. Question 2.
A charge of 8860 C flows through an electric circuit in 2 min and 40 s. Calculate the magnitude of current in circuit.  