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Relationship between power and resistance is represented either in Series or Parallel. Resistance is a particle that helps us to measure opposition to current flow in an electrical circuit. It is measured in ohms (Ω).
Whereas, Power is the rate of doing work. It is directly and inversely proportional to resistance.Relation between Power and Resistance mathematically-
P = I2R
- P = Power measured in watt
- R = Resistance measured in ohms
- I = Electric current measured in coulombs
P = \(\frac{V^2}{R}\)
- P = Power measured in watt
- R = Resistance measured in ohms
- V is the electric potential measured in volts
It implies-
- When power increases, the resistance will also increase keeping current I constant.
- When Resistance decreases, Power also reduces keeping current I constant.
Ques. A 220 V, 100W Bulb is connected to a 110V source. Calculate the Power consumed by the bulb.
- 10W
- 15W
- 20W
- 25W
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Ans. D) 25W
Explanation- Electric power is the rate at which electrical energy is dissipated into the other forms of energy.
Given: Potential difference (V) = 220 V,
Power of the bulb (P)= 110W
Voltage= 110V
Resistance of the bulb is calculated as,
⇒ R = \(\frac{V^2}{P}\) = \(\frac{(220)^2}{100}\) = 484Ω
Power consumed by the bulb is calculated as,
⇒ P = \(\frac{V^2}{R}\) = \(\frac{(110)^2}{484}\) = 25 W
Ques. The instrument _____ is used for detecting electric current is.
- Galvanometer
- Tube tester
- Altimeter
- Fathometer
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Ans. A) Galvanometer
Explanation- A galvanometer is used to detect current in an electric circuit. It is mainly used in bridges and potentiometers where they indicate the null deflection or zero current.
Ques. An ammeter is connected in ____ with the circuit.
- Parallel
- Series
- Both parallel and series
- None of the above
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Ans. B) Series
Explanation- An ammeter is a device which is used to measure the current in a circuit. It is generally connected in series in a circuit. It is because the current remains the same when devices are connected in series.
Ques. The SI unit of electrical conductance is______.
- Ohm
- Siemens
- Ohm meters
- Ampere
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Ans. B) Siemens
Explanation- The SI unit of conductance = 1/9The SI unit of resistance)= 1/Ω=-1= Siemens.
- Ohm is the SI unit of resistance.
- Ampere is the SI unit of current
Ques. A current of 5 A is drawn by filament of an electrical bulb for 2 minutes. Find the amount of electric charge that flows through the circuit.
- 300C
- 450C
- 500C
- 600C
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Ans. D) 600C
Explanation- It is given that I= 5 A and t= 2 min= 120s
- The total charge on the conductor is given by q = It
⇒ Q = It
⇒ Q = 5 120 = 600C
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Ques. The poorest in electrical conductivity among the following metal is
- Silver
- Copper
- Gold
- Aluminium
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Ans. D) Aluminium
Explanation- In the given options, Silver has the highest conductivity and aluminium has the least. On a scale of 0 to 100 for electrical conductivity the silver ranks 100 with copper at 97 and gold at 76, aluminium at 60.
Ques. A moving coll galvanometer can be converted into a ammeter by connecting the moving coil galvanometer.
- Low resistance in series
- Low resistance in parallel
- High resistance in parallel
- High resistance in series
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Ans. B) Low resistance in parallel
Explanation- A moving coil galvanometer can be converted into an ammeter by connecting a low resistance in parallel to the moving galvanometer.
Ques. The temperature coefficient of a wire is 0.00125 per C. At 300k the resistance is 1 ohm. Then the resistance of the wire at 2 ohms will be?
- 1154 K
- 1100 K
- 1400 K
- 1127 K
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Ans d) 1127 K
Explanation: Its given that a = 0.00125 per ▫C
R300K= 1Ω, i.e.
T = 300 – 273 = 27℃
1 = R0(1 + a x 27) – (1)
Resistance = 2Ω for temperature T.
Hence,
2 = R0(1 + aT) - (2)
(1) / (2)
(1 + aT) = 2(1 + a x 27)
a(T – 54) = 1
T – 54 = 800
T = 854
T = 854 + 273 = 1127K
Ques. The resistivity of a conductor depends on?
- Material
- Area of cross section
- Length
- All of the given options
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Ans. A) Material
Explanation- Since, the resistivity of any conductor is the property of the material. So it is independent of the shape and the size.
It depends on the material of the conductor.
Ques. The direction of flow of electric current is from
- Negative terminal to Positive Terminal
- Positive Terminal to Negative Terminal
- Both
- None of these
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Ans. B) Positive Terminal to Negative Terminal
Explanation- The direction of the conventional current corresponds to the direction of positive charges which is higher potential (positive) to lower potential (negative).
Electric current is associated with the movement of electrons from lower potential (negative) to higher potential (positive). Therefore, the direction of electric current is opposite to that of conventional current.
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