CBSE Class 10 Physics HOTs Electricity Set 02

TOPIC : Electric Current and Circuit

Question. The electric current in the conductor exists only when the quantity that flows through it is
(a) electric charge
(b) air current
(c) water current
(d) all of the options
Answer: (a) electric charge

Question. Amount of charge flowing through a particular area in unit time is called
(a) electric charge
(b) electric current
(c) electric potential
(d) all of the options
Answer: (b) electric current

Question. The unit of electric charge is
(a) ampere
(b) joule
(c) coulomb
(d) ohm
Answer: (c) coulomb

Question. Choose the incorrect statements from the following:
(a) Charge on the body may be positive or negative.
(b) Electric charge is scalar quantity.
(c) Coulomb is the cgs unit of charge.
(d) A continuous and closed path is required for the flow of electric charge.
Answer: (c) Coulomb is the cgs unit of charge.

Question. The particles that constitute the flow of charge through a conductor is
(a) electrons
(b) protons
(c) neutrons
(d) atoms
Answer: (a) electrons

Question. The materials which allow electric current to pass through them easily are called
(a) conductors
(b) insulators
(c) semiconductors
(d) alloys
Answer: (a) conductors

Question. Conventionally, direction of electric current in the circuit is taken as the direction of flow of
(a) negative charge
(b) atoms
(c) positive charge
(d) neutrons
Answer: (c) positive charge

Question. The relation between electric current and electric charge is
(a) Q = I/t
(b) t = QI
(c) I = Qt
(d) I = Q/t
Answer: (d) I = Q/t

Question. The number of electrons constituting one coulomb of charge is
(a) \( 6 \times 10^{18} \)
(b) \( 1.6 \times 10^{–19} \)
(c) \( 6 \times 10^{–18} \)
(d) \( 1.6 \times 10^{19} \)
Answer: (a) \( 6 \times 10^{18} \)

Question. SI unit of electric current is
(a) ohm
(b) ampere
(c) volt
(d) joule
Answer: (b) ampere

Question. The value of 1 mA and 1 \( \mu \)A are
(a) \( 10^{–6} \) and \( 10^{–3} \) A respectively
(b) \( 10^{–6} \) and \( 10^{–9} \) A respectively
(c) \( 10^{–3} \) and \( 10^{–6} \) A respectively
(d) \( 10^{3} \) and \( 10^{6} \) A respectively
Answer: (c) \( 10^{–3} \) and \( 10^{–6} \) A respectively

Question. State two properties of charge.
Answer: Properties of Charge:
(i) The basic idea about positive and negative charge is that “like charges repel and unlike charges attract each other.
(ii) Electric charge can neither be created nor destroyed but it can transfer from one body to another i.e., total electric charge in an isolated system is conserved.
(iii) Total charge on a body is equal to the algebraic sum of all the charges located on that body.
(iv) Charges are quantized i.e., charge on a body is an integral multiple of the charge of electron or proton.
Therefore, the total charge Q on a body is given by \( Q = ne \)
Where, \( e = 1.6 \times 10^{–19} \text{ coulomb} \), \( n = \pm1, \pm2, \pm3 \), and so on. (any two)

Question. Name the two fundamental particles which carry equal and opposite charges. What amount of charge they carry?
Answer: Electron and proton
Charge on electron = \( –1.6 \times 10^{–19} \text{ C} \)
Charge on proton = \( +1.6 \times 10^{–19} \text{ C} \)

Question. How many electrons must be removed from a conductor, so that it acquires a charge of \( 4.8 \text{ } \mu\text{C} \)?
Answer: Here \( q = 4.8 \text{ } \mu\text{C} = 4.8 \times 10^{–6} \text{ C} \)
Charge on electron, \( e = 1.6 \times 10^{–19} \text{ C} \)
Using, \( q = ne \)

\( \implies \) \( n = \frac{q}{e} = \frac{4.8 \times 10^{–6}}{1.6 \times 10^{–19}} = 3 \times 10^{13} \)
So, \( n = 3 \times 10^{13} \) electrons

Question. In how much time \( 9 \times 10^3 \) coulomb of charge will flow, if an electric current of 6 A is drawn by an electrical appliance?
Answer: Using, \( Q = It \)

\( \implies \) \( 9 \times 10^3 = 6 \times t \)
\( \therefore t = \frac{9 \times 10^3}{6} = 1500 \text{ s} = 25 \text{ min} \)

Question. A current of 1 A is drawn by a filament of an electric bulb. Calculate the number of electrons passing through the cross-section of the filament in 30 minutes.
Answer: Given: \( I = 1 \text{ A} \), \( t = 30 \text{ min} = 30 \times 60 = 1800 \text{ sec} \)
Using, \( Q = It = 1 \times 1800 = 1800 \text{ C} \)
Now, \( Q = ne \)

\( \implies \) \( 1800 = n \times 1.6 \times 10^{–19} \)

\( \implies \) \( n = \frac{1800}{1.6 \times 10^{–19}} = 1125 \times 10^{19} \)

\( \implies \) \( n = 1.125 \times 10^{22} \)
Hence, number of electrons passing through the filament in 30 minutes = \( 1.125 \times 10^{22} \) electrons \( \approx 10^{22} \) electrons

Question. What is meant by electric current? Name and define its SI unit. In a conductor electrons are flowing from B to A. What is the direction of conventional current? Give justification for your answer. A steady current of 1 ampere flows through a conductor. Calculate the number of electrons that flows through any section of the conductor in 1 second. (Charge on electron \( 1.6 \times 10^{–19} \text{ coulomb} \)).
Answer:

• Electric Current: The amount of charge ‘Q’ flowing through a particular area of cross section in unit time ‘t’ is called electric current. i.e. Electric current, \( I = \frac{Q}{t} \)
• SI unit of electric current is ampere.
• One ampere of current is that current which flow when one coulomb of electric charge flowing through a particular area of cross-section of the conductor in one second, i.e. 1A = 1 Cs⁻¹.
• The direction of conventional current is A to B, i.e. opposite to the direction of flow of electrons. In a metal, flow of electrons carrying negative charge constitutes the current. Direction of flow of electrons gives the direction of electronic current by convention, the direction of flow of positive charge is taken as the direction of conventional current.
• Charge, \( q = It = ne \)
  \( n = \frac{It}{e} = \frac{1 \times 1}{1.6 \times 10^{–19} \text{ C}} = \frac{10^{19}}{1.6} = 6.25 \times 10^{18} \text{ electrons} \)

PRACTICE QUESTIONS

Question. The device which measures the electric current in the circuit is
(a) ammeter
(b) voltmeter
(c) galvanometer
(d) all of the options
Answer: (a) ammeter

Question. If electrons flow in a conductor from its one end ‘A’ to other end ‘B’, the current will flow from
(a) A to B
(b) B to A
(c) mid-point of the conductor to end A
(d) mid-point of the conductor to end B
Answer: (b) B to A

Question. Calculate the amount of charge that would flow in one hour through an element of electric gyser drawing a current of 2 A.
Answer: \( I = 2 \text{ A} \), \( t = 1 \text{ hr} = 3600 \text{ s} \). \( Q = It = 2 \times 3600 = 7200 \text{ C} \).

Question. How long would a charge of 900 C move through a closed circuit at a steady rate of \( 15 \text{ Cs}^{–1} \)?
Answer: \( Q = 900 \text{ C} \), \( I = 15 \text{ A} \). \( t = \frac{Q}{I} = \frac{900}{15} = 60 \text{ s} \).

Question. \( 5.40 \times 10^{21} \) electrons flow through the element of electric iron in 3 minutes.
(a) How much charge flows through this appliance?
(b) Calculate the current flow through it in 3 min.
Answer: (a) \( Q = ne = 5.40 \times 10^{21} \times 1.6 \times 10^{–19} = 864 \text{ C} \).
(b) \( I = \frac{Q}{t} = \frac{864}{180} = 4.8 \text{ A} \).

TOPIC : Electric Potential and Potential Difference

Question. The amount of work done to move a unit charge from one point to the other in an electric circuit carrying some current is called as
(a) power
(b) electric potential difference
(c) electric current
(d) resistance
Answer: (b) electric potential difference

Question. Amount of work done needed for each coulomb of charge between two points in a current carrying conductor having potential difference of 1 V is
(a) 1 Joule
(b) 1 Watt
(c) 1 Ohm
(d) 1 kW
Answer: (a) 1 Joule

Question. 1 volt is equal to
(a) \( 1 \text{ Js}^{–1} \)
(b) \( 1 \text{ JC}^{–1} \)
(c) \( 1 \text{ Nm}^{–1} \)
(d) \( 1 \text{ CJ}^{–1} \)
Answer: (b) \( 1 \text{ JC}^{–1} \)

Question. The source of energy which provide the potential difference for the steady flow of current in the electric circuit is
(a) ammeter
(b) voltmeter
(c) battery
(d) all of the options
Answer: (c) battery

Question. Potential difference between two points in an electric circuit is measured by an instrument called
(a) battery
(b) ammeter
(c) galvanometer
(d) voltmeter
Answer: (d) voltmeter

Question. Which of the following expressions correctly represent the potential difference between two points in an electric circuit?
(a) \( V = \frac{W}{Q} \)
(b) \( V = \frac{Q}{W} \)
(c) \( V = Q \times W \)
(d) \( Q = VW \)
Answer: (a) \( V = \frac{W}{Q} \)

Question. A battery of 10 volt carries 20,000 C of charge through a resistance of 20 \( \Omega \). The work done in 10 seconds is
(a) \( 2 \times 10^3 \text{ joule} \)
(b) \( 2 \times 10^5 \text{ joule} \)
(c) \( 2 \times 10^4 \text{ joule} \)
(d) \( 2 \times 10^2 \text{ joule} \)
Answer: (b) \( 2 \times 10^5 \text{ joule} \)

Question. When two points at different potential are connected across the ends of a conductor, the electric current flows through it from the point
(a) at a higher potential to a lower potential
(b) at a lower potential to a higher potential
(c) at zero potential to the some potential point
(d) cannot say
Answer: (a) at a higher potential to a lower potential

Question. Why must voltmeter have high resistance?
Answer: The voltmeter connected in parallel across the component, such as resistor must have high resistance so that a very small current passes through it and the potential difference across that component is not affected.

Question. When a particle of charge \( 10 \text{ } \mu\text{C} \) is brought from infinity to a point in the electric field, 10 mJ work is done by the external forces. What is the potential at that point?
Answer: Given \( Q = 10 \text{ } \mu\text{C} = 10 \times 10^{–6} \text{ C} = 10^{–5} \text{ C} \)
\( W = 10 \text{ mJ} = 10 \times 10^{–3} \text{ J} = 10^{–2} \text{ J} \)
At infinity potential is zero
Using, \( V_A – V_B = \frac{W}{Q} \)

\( \implies \) \( V – V_\infty = \frac{W}{Q} \) (let \( V_A = V, V_B = V_\infty \))

\( \implies \) \( V – 0 = \frac{10^{–2}}{10^{–5}} \)

\( \implies \) \( V = 10^{–2+5} = 10^3 = 1000 \text{ V} \)

Question. (a) State the relation between work, charge and potential difference for an electric circuit.
(b) Calculate the potential difference between the two terminals of a battery if 100 J of work is required to transfer 20 C of charge from one terminal of the battery to the other.
Answer: (a) Potential difference = \( \frac{\text{Work done}}{\text{Charge}} \)
\( V_A – V_B = \frac{W}{Q} \)
(b) \( Q = 20 \text{ C}, W = 100 \text{ J} \)
\( \therefore \) Potential difference, \( V = \frac{W}{Q} = \frac{100}{20} \)

\( \implies \) \( V = 5 \text{ volt} \)

Question. Calculate the amount of work done in shifting of charge of 2 C from a point A to B having potentials +10 V and –5 V respectively.
Answer: \( Q = 2 \text{ C}, V_A = +10 \text{ V}, V_B = –5 \text{ V} \)
Using \( V_A – V_B = \frac{W}{Q} \)

\( \implies \) \( 10 – (–5) = \frac{W}{2} \)

\( \implies \) \( W = 30 \text{ J} \)

Question. Define 1 volt. Express it in terms of SI unit of work and charge. Calculate the amount of energy consumed in carrying a charge of 1 coulomb through a battery of 3 V.
Answer: When 1 joule of work is done in carrying 1 coulomb of charge, from infinity to a point in the electric field, then potential at that point is called 1 volt.
Potential difference between two points is \( V = \frac{W}{Q} \)
or \( W = Q \times V = 1 \times 3 = 3 \text{ J} \)

Question. A continuous and closed path of an electric current is called
(a) an electric circuit
(b) electric pressure
(c) circuit element
(d) All of the options
Answer: (a) an electric circuit

Question. The position of switch/key in an electric circuit is
(a) right side of the cell or battery
(b) left side of the cell or battery
(c) anywhere in the circuit
(d) before the circuit element
Answer: (c) anywhere in the circuit

Question. The function of switch in an electric circuit is
(a) to make the circuit closed
(b) to make the circuit open
(c) both (a) and (b)
(d) neither (a) nor (b)
Answer: (c) both (a) and (b)

Question. Which of the following is an essential element in an electric circuit?
(a) Connecting wire
(b) Bulb
(c) An ammeter
(d) A plug key
Answer: (a) Connecting wire

Question. A schematic diagram drawn by using symbols which represent electrical components is called
(a) electric diagram
(b) circuit diagram
(c) element diagram
(d) current diagram
Answer: (b) circuit diagram