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Substances that have constant resistance over a wide range of voltages are

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Important Questions on Current Electricity

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Physics>Electricity and Magnetism>Current Electricity>Limitations of Ohm's Laws

A copper wire with a cross-section area of

2 \times 10^{- 6} m^{2}

has a free electron density equal to

5 \times 10^{22} {cm}^{- 3} .

If this wire carries a current of

16 A

, the drift velocity of the electron is

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Physics>Electricity and Magnetism>Current Electricity>Limitations of Ohm's Laws

Ohm's law is applicable to

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Physics>Electricity and Magnetism>Current Electricity>Limitations of Ohm's Laws

The resistivity of potentiometer wire is

40 \times 10^{- 8} Ω m

and its area of cross-section is

8 \times 10^{- 6} m^{2}

. If

0.2 A

current is flowing through the wire, the potential gradient of the wire is

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Physics>Electricity and Magnetism>Current Electricity>Limitations of Ohm's Laws

{kgm}^{2} s^{- 3} A^{- 2}

is the SI unit of

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Physics>Electricity and Magnetism>Current Electricity>Limitations of Ohm's Laws

The device or substances which DO NOT obey ohm's law is/are

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Physics>Electricity and Magnetism>Current Electricity>Limitations of Ohm's Laws

The number of free electrons per

100 mm

of ordinary copper wire is

2 \times 10^{21}

. Average drift speed of electrons is

0.25 mm s^{- 1}

. The current flowing is

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Physics>Electricity and Magnetism>Current Electricity>Limitations of Ohm's Laws

Suppose the drift velocity

v_{d}

in a material varied with the applied electric field E as

v_{d} \propto \sqrt{E}

. Then

V - I

graph for a wire made of such a material is best given by:

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Physics>Electricity and Magnetism>Current Electricity>Limitations of Ohm's Laws

Though the electron drift velocity is small and electron charge is very small, a conductor can carry an appreciably large current because

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Physics>Electricity and Magnetism>Current Electricity>Limitations of Ohm's Laws

In the circuit shown, the cells

A

and

B

have negligible resistances for

V_{A} = 12 V, R_{1} = 500 Ω

and

R = 100 Ω

. The galvanometer

(G)

shows no deflection. The value of

V_{B}

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Physics>Electricity and Magnetism>Current Electricity>Limitations of Ohm's Laws

Drift speed of electrons, when

1.5 A

current flows in a copper wire of cross section

5 {mm}^{2}

v_{d} .

If the electron density in copper is

9 \times 10^{28} m^{- 3}

the value of

v_{d}

mm s^{- 1}

is close to (Take charge of an electron to be

= 1.6 \times 10^{- 19} C

)

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Physics>Electricity and Magnetism>Current Electricity>Limitations of Ohm's Laws

To verify Ohm’s law, a student connects the voltmeter across the battery as shown in the figure. The measured voltage is plotted as a function of the current, and the following graph is obtained:
Question Image

V_{o}

is almost zero, identify the correct statement:

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Physics>Electricity and Magnetism>Current Electricity>Limitations of Ohm's Laws

Ohm's Law is applicable to

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Physics>Electricity and Magnetism>Current Electricity>Limitations of Ohm's Laws

A current of

5 A

passes through a copper conductor (resistivity

= 1.7 \times 10^{- 8} Ω m

) of radius of cross-section

5 m m

. Find the mobility of the charges if their drift velocity is

1.1 \times 10^{- 3} m s^{- 1}

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Physics>Electricity and Magnetism>Current Electricity>Limitations of Ohm's Laws

In the circuit shown below, a student performing Ohm's law experiment accidentally puts the voltmeter and the ammeter as shown in the circuit below; the reading in the voltmeter will be close to
Question Image

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Physics>Electricity and Magnetism>Current Electricity>Limitations of Ohm's Laws

In the figure shown, what is the current (in ampere) drawn from the battery? You are given:
$R_{1} = 15 Ω, R_{2} = 10 Ω, R_{3} = 20 Ω, R_{4} = 5 Ω, R_{5} = 25 Ω, R_{6} = 30 Ω, E = 15 V$
Question Image

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Physics>Electricity and Magnetism>Current Electricity>Limitations of Ohm's Laws

When a diode is forward biased, it has a voltage drop of

0.5 V

. the safe limit of current through the diode is

10 mA

. If a battery of emf

1.5 V

is used in the circuit, the value of minimum resistance to be connected in series with the diode so that the current does not exceed the safe limit is :

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Physics>Electricity and Magnetism>Current Electricity>Limitations of Ohm's Laws

A steady current flows in a metallic conductor of non-uniform cross section. The quantity/quantities that remains/remain constant along the length of the conductor is/are

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Physics>Electricity and Magnetism>Current Electricity>Limitations of Ohm's Laws

When

5 V

potential difference is applied across a wire of length

0.1 m

, the drift speed of electrons is

2.5 \times 10^{- 4} m s^{- 1}

. If the electron density in the wire is

8 \times 10^{28} m^{- 3}

, the resistivity of the material is close to:

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Physics>Electricity and Magnetism>Current Electricity>Limitations of Ohm's Laws

Assertion: The drift velocity of electrons in a metallic wire will decrease, if the temperature of the wire is increased.

Reason: On increasing the temperature, conductivity of metallic wire decreases.

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Physics>Electricity and Magnetism>Current Electricity>Limitations of Ohm's Laws

$I - V$ characteristic of a copper wire of length $L$ and area of cross-section $A$ is shown in figure. The slope of the curve becomes

Question Image

Substances that have constant resistance over a wide range of voltages are

Important Questions on Current Electricity

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