Short Questions Answer
1. What is meant by an electric circuit?
Answer: A continuous and closed path of an electric current is called an electric circuit.
2. Define one ampere.
Answer: One ampere is the current when one coulomb of charge flows through a conductor in one second.
3. What instrument is used to measure electric current?
Answer: An ammeter is used to measure electric current.
4. What is the SI unit of electric potential difference?
Answer: The SI unit of potential difference is volt (V).
5. Define one volt.
Answer: One volt is the potential difference when one joule of work is done in moving one coulomb of charge.
6. What does a voltmeter measure?
Answer: A voltmeter measures the potential difference between two points in a circuit.
7. State Ohm’s law.
Answer: Ohm’s law states that the potential difference across a conductor is directly proportional to the current through it if temperature remains constant.
8. What is the SI unit of resistance?
Answer: The SI unit of resistance is ohm (Ω).
9. On what factors does the resistance of a conductor depend?
Answer: Resistance depends on the conductor’s length, area of cross-section, and the material.
10. What is the heating effect of electric current?
Answer: The conversion of electrical energy into heat energy when current flows through a resistor is called the heating effect of electric current.
11. What is the formula for electric power?
Answer: P = VI = \(I^2\)R = \(\frac{V^2}{R}\)
12. What is the commercial unit of electrical energy?
Answer: The commercial unit is kilowatt-hour (kWh).
13. What material is used for making the filament of an electric bulb?
Answer: Tungsten is used for making the filament of electric bulbs.
14. Why are fuses used in electric circuits?
Answer: Fuses protect electrical circuits by stopping excessive current flow that could cause damage.
15. What type of connection is used in domestic wiring – series or parallel?
Answer: Parallel connection is used in domestic wiring.
Long Questions Answer
1. Define electric current. Write its formula and SI unit.
Answer: Electric current is the rate of flow of electric charge through a conductor.
Formula: I = \(\frac{Q}{t}\)
SI Unit: Ampere (A)
2. Explain the concept of potential difference with a suitable example.
Answer: Potential difference between two points is the work done to move a unit charge from one point to another.
Formula: V = \(\frac{W}{Q}\)
Example: In a battery, chemical energy produces a potential difference across its terminals, causing current to flow.
3. State Ohm’s law and derive its mathematical expression.
Answer: Ohm’s law states that the current (I) through a conductor is directly proportional to the potential difference (V) across its ends, provided temperature remains constant.
V∝I or 𝑉 = IR
Here, R is the constant of proportionality called resistance.
4. On what factors does the resistance of a conductor depend?
Answer: Resistance R depends on:
- Length of conductor (R ∝ l)
- Area of cross-section (R ∝ 1/A)
- Nature of material
- Temperature of the conductor
5. Derive the relation for equivalent resistance when resistors are connected in series.
Answer: When resistors \(R_1\),\(R_2\),\(R_3\) are connected in series, the same current flows through each resistor, and total potential difference is:
V = \(V_1\)+\(V_2\)+\(V_3\) = I\(R_1\)+I\(R_2\)+I\(R_3\) = I(R1+R2+R3)
Therefore, \(R_s\) = \(R_1\)+\(R_2\)+\(R_3\)
6. Derive the relation for equivalent resistance when resistors are connected in parallel.
Answer: For resistors \(R_1\),\(R_2\),\(R_3\) in parallel, potential difference across each is same, but total current
I = \(I_1\)+\(I_2\)+\(I_3\)
Using I = \(\frac{V}{R}\)
\(\frac{V}{R_p}\) = \(\frac{V}{R_1}\) + \(\frac{V}{R_2}\) + \(\frac{V}{R_3}\)
Therefore, \(\frac{1}{R_p}\) = \(\frac{1}{R_1}\) + \(\frac{1}{R_2}\) + \(\frac{1}{R_3}\)
7. What is Joule’s law of heating? Write its applications.
Answer: Joule’s law states that heat produced in a resistor is directly proportional to the square of current, resistance, and time.
Formula: H = \(I^2\)Rt
Applications:
- Electric heaters and irons
- Electric bulbs
- Electric fuse protection
8. Explain the working and function of an electric fuse.
Answer: A fuse is a safety device used to prevent excessive current in a circuit. It consists of a wire with a low melting point. When current exceeds the safe limit, the fuse wire melts and breaks the circuit, preventing damage.
9. Define electric power and derive its formula in different forms.
Answer: Electric power is the rate of doing electrical work or energy consumed per unit time.
P = VI
Using Ohm’s law 𝑉 = 𝐼𝑅
P = \(I^2\)R or 𝑃 = \(\frac{V^2}{R}\)
10. What are the advantages of connecting electrical devices in parallel?
Answer:
- Each device gets the same potential difference.
- If one device fails, others continue to work.
- The total resistance of the circuit decreases.
- Each device can be operated independently.
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