Ohm’s Law Questions

Ohm’s Law Questions are given in the chapter Current Electricity in CBSE Class 12 Physics Syllabus. This article helps students to refer to and learn some of the important questions related to Ohm’s Law.

Ohm’s Law states that the potential difference across the two ends of a conductor is directly proportional to the current flowing through the circuit at constant temperature conditions. Mathematically,

Voltage (V) ∝ Current (I)

⇒ V = IR 

where R is the constant Resistance.

The unit of resistance is Ohms, Ω.

Ohms Law Explained 

Ohms law video

Read More: NCERT Solutions Class 12 Physics: Current Electricity 

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Important Questions on Ohm’s Law 

Ques 1: What is Ohm’s law? (3 marks)

Ans: Ohm’s law was introduced by George Simon Ohm and it gives the relationship between current, voltage, and resistance in an electrical circuit. The law states that the amount of steady current flowing through many materials is directly proportional to the potential difference across the materials. The ratio V/I hence remains a constant. The proportionality constant is called resistance. The SI unit of resistance is Ohms, Ω

Ques 2: What are the applications of Ohm’s Law? (3 marks)

Ans: Listed below are the applications of Ohm’s Law:

• To find voltage, resistance, and current in an electric circuit.
• To maintain the desired voltage drop across the electrical components in the circuit
• In DC Ammeters and DC shunts to divert current.
• To know the power consumption in electrical heaters
• For deciding the size of the resistors

Ques 3: Determine the current in a 75 W light bulb that is connected to 120V. (2 marks)

Ans: Power of the electric bulb= 75 W

Voltage = 120V

From Ohm’s Law, V=IR or P=IV

Therefore,

I = P/V 

I = 75/20

= 0.625 A.

Ques 4: In a purely resistive electrical appliance, the emf source is 10 V. The current flowing through it is 1 A. If the wires are resistance-free, calculate the resistance of the appliance. (2 marks)

Ans: From Ohm’s law we know that 

V= IR

Therefore

R= V/I

Substituting we get, 

R = 10/1

Therefore the resistance of the electrical appliance is 10 Ω

Ques 5: The following circuit has resistors R₁ and R₂ connected in series. The resistance values are 5 Ω and 10 Ω respectively. If the voltage across R₁ is 4 V, calculate the current through R₂ and across the same resistor. (3 marks)

Ans: From Ohm’s Law,

V= IR

If I₁ is the current passing through R₁

Substituting we get,

 We use Ohm’s law V = R I to find the current I₁ passing through R₁.

4= 5 I₁

Therefore, 

I₁ = 4 / 5 = 0.8 A

When the resistors are in series, the current passing through them is the same. Thus I₂ through R₂ is 0.8 A.

V₂ = R₂I₂

= 10 x 0.8

=8V

Do Check Out: 

Ques 6: List down the limitations of Ohm’s Law. (5 marks)

Ans: Listed below are the limitations of Ohm’s Law:

• This law is not applicable for unilateral elements as the current flows only in a single direction.
• In non-linear electrical components, the voltage and current values are not constant which means the resistance changes with different current and voltage values. An example is a thyristor. 
• The voltage and current in an electrical circuit depend on the sign of V (+ or -). Thus reversing the direction and keeping the magnitude fixed does not produce a current of the same magnitude and direction. Example diodes.
• Ohm’s Law is applicable only for metallic conductors.

Ques 7: What is the importance of Ohm’s Law? (5 marks)

Ans: Ohm’s Law explains the relation between the voltage, current, and resistance in an electrical circuit. Some of the important features of this law are:

• The number of resistors can be altered thereby allowing to control the current flow. The more the number of resistors, the lower will be the current in the circuit.
• The circuit power can be evaluated by using this law, P=IV. This thus ensures that the circuit provides enough power.
• The voltage drop across any component in the circuit can be easily evaluated using Ohm’s Law and Kirchoff’s rules.

Ques 8: If the resistance in the circuit is halved, keeping the potential difference is kept constant. What will be the change in the current? (3 marks)

Ans: From Ohm’s law, 

V=IR

V₁= I₁ R₁

V₂ = I₂ R₂

Thus,

 I₁ R₁ = I₂R₂

=I₂R₁/2

I₂= I₁ R₁/(R₁/2)

=2I₁

Ques 9: Which conductor has a linear V-I relationship? (1 mark)

Ans: Ohmic conductors obey Ohm’s Law. The V-I relationship in these conductors is hence linear in nature. 

Ques 10: Give an example of a non-Ohmic conductor. (1 mark)

Ans: Silicon is an example of a non-ohmic conductor. Silicon displays a non-linear behavior. The current rescues after a value of current. Hence the V-I plot is non-linear in nature. 

Ohm’s Law Questions can be studied along with Ohm’s Law MCQ for a better understanding of the concept.

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