# ICSE Class 10th Physics 9 – Current Eletricty MCQs

#### In an experiment to verify ohm's law current in the circuit is varied by: (i) changing the battery (ii) varying the resistance in rheostat

In an experiment to verify ohm's law current in the circuit is varied by varying the resistance in rheostat.

#### The resistivity of a wire:

Resistivity of a wire is independent of length, cross section and mass of the wire. It is the intrinsic property of the material of the wire.

#### The decrease of resistance in parallel combination is due to:

When two resistors are connected in parallel, the effective area of a cross-section through which the current can pass, increases. Since the resistance of a wire is given by i.e., inversely proportional to the area of cross-section. Therefore, any increase in the area of cross-section decreases the resistance.

#### In a circuit, the amount of current drawn from the cell is increased. Due to this, the e.m.f. of the cell ____ and the terminal voltage of the cell ____.

Due to this, the e.m.f. of the cell remains the same and the terminal voltage of the cell decreases. Electromotive force (e.m.f.) is the characteristic of a cell; it is independent of the amount of current drawn from the cell. Hence, change in current drawn does not affect the e.m.f. of the cell. The terminal voltage of a cell depends on the amount of current drawn from the cell. When a larger current is drawn from the cell, more work is done in moving the charges from one electrode to the other through the electrolyte. The voltage drop increases and thus the terminal voltage decreases.

#### When a number of resistors are connected in parallel, then their resultant resistance is ______________ the smallest individual resistance.

When a number of resistors are connected in parallel, then their resultant resistance is less than the smallest individual resistance.

#### In the circuit that is built to verify Ohm's law, ____.

In the circuit that is built to verify Ohm's law, the voltmeter is connected in parallel and the ammeter is connected in series.

#### . The resistance offered by the electrolyte inside the cell to the flow of current of magnitude 1.25 A is 2 Ω. The voltage drops in the internal resistance of the cell will be____.

The voltage drop in the internal resistance of the cell will be 2.5 V. By definition, the internal resistance(r) is the resistance offered by the electrolyte inside the cell to the flow of current. Hence in this case, r = 2 Ω The current(I) = 1.25 A The work done in carrying a unit charge through the electrolyte is called the voltage drop (v). r, v and I are related as follows - v = Ir Thus, V = 1.25 A × 2 Ω = 2.5 V

#### A 9 V battery has an internal resistance of 12 Ω. The potential difference across its terminals when it is supplying a current of 50 mA is ____.

The potential difference across its terminals when it is supplying a current of 50 mA is 8.4 V. Given: E.m.f. of battery (E) = 9 V Internal resistance (r) = 12 Ω Current(I) = 50 mA = 50 × 10-3 A = 5 × 10-2 A Potential difference across terminals = E – Ir = 9 V - (5 × 10-2 A × 12 Ω) = (9 - 0.6) V = 8.4 V

#### How much work is done, when 1 coulomb of charge moves against a potential difference of 1 volt?

v = W/Q =1V = W/Q ∴W = 1J

#### A uniform conducting wire offers a resistance of 60 Ω. It is cut into 12 equal parts and 6 of them are connected in parallel and remaining 6 are connected in series. This parallel bundle is connected in series with the series chain. Then, find the net resistance.

Each part will have r/12 resistance = 60 Ω/12 = 5 Ω NET RESISTANCE Of 6 resistances in parallel = 5/6 Ω NET RESISTANCE Of 6 resistances in series = 30 Ω Thus, net resistance of parallel bundle connected in series with the series chain R = 5/6 Ω + 30 Ω = 185/6 Ω = 30.84 Ω

#### An electrical cell has an e.m.f. of 12 V. A potential difference of 11.5 V appears across the terminals when a current of 0.25 A is drawn from it. The internal resistance of the cell is ____.

The internal resistance of the cell is 2 Ω. Given: e.m.f. of cell(E) = 12 V Potential difference(V) = 11.5 Current through the circuit(I) = 0.25 A Let 'r' be the internal resistance of the cell. Thus, V = E – Ir Substituting the values, 11.5 V = 12 V - (0.25 A × r) 0.25 r = 12 - 11.5 Or, r = 0.5/0.25 = 2 Ω

#### The equivalent unit for measuring the electromotive force of a cell is ____.

The equivalent unit for measuring the electromotive force of a cell is J/C. The electromotive force (e.m.f.) of a cell is defined as the energy spent or work done in taking a unit positive charge around the complete circuit of the cell. If work W is done in taking a test charge q0 around the complete circuit of the cell, then e.m.f. of cell E = W/q0 Work is measured in joules (J) and the unit for charge is coulomb (C). Thus, the equivalent unit for e.m.f. is J/C.

#### The graph plotted between voltage (taken on X axis) and current (taken on Y axis) in an experiment to verify Ohm's law for an ohmic conductor is ____.

The graph plotted between voltage (taken on X axis) and current (taken on Y axis) in an experiment to verify Ohm's law for an ohmic conductor is an inclined straight ine passing through the origin.

#### The slope of a straight line graph plotted between potential difference along the X axis and current along the Y axis in an experiment to verify Ohm's law gives ____ of the conductor.

The slope of a straight line graph plotted between potential difference along the X axis and current along the Y axis in an experiment to verify Ohm's law gives resistance of the conductor.

#### In an experiment verifying Ohm's law, it is a must to maintain constant ____.

In an experiment verifying Ohm's law, it is a must to maintain constant temperature.

#### When a number of resistors are connected in parallel, then their resultant resistance is ______________ the smallest individual resistance.

When a number of resistors are connected in parallel, then their resultant resistance is less than the smallest individual resistance.

#### The voltage drop in a cell increases when the concentration of the electrolyte is increased for the same current drawn. This is because ____.

This is because the internal resistance increases. The internal resistance of a cell depends on the concentration of the electrolyte in the cell. Higher the concentration of the electrolyte, greater is the internal resistance. The voltage drop (v) in a cell is directly proportional to the internal resistance (r) of the cell. Hence, if the internal resistance increases, the voltage drop also increases for the same current (I) drawn from the cell; i.e. v = Ir

#### The ammeter and the battery in the sketch to the right have negligible resistance. The resistors are in parallel. What will happen to the ammeter and voltmeter readings when switch S is closed?

When the circuit is closed, the resistances get connected in parallel; hence the net resistance decreases thus increasing the current through the ammeter. The voltmeter is connected across the battery and since the battery voltage does not decrease, the reading in voltmeter remains unchanged.

#### A conductor of resistance 3 Ohm is stretched uniformly till its length is doubled. If the wire is bent in the form of an equilateral triangle, find the resistance across any side.

Here, R = Î¡l/A or, R = Î¡l^{2}/V or, R1/R2 = l_{1 }^{2 }/ l_{2 }^{2 }or R2 = (4 l^{2 }/ l^{2 }) x R or R2 = 4R or R2 = 12 Ohm Here, R (net) = R1R2/ ( R1 + R2) or, R (net) = 8/3 Ohm

#### The true statement from the following is ____.

The true statement is the e.m.f. of a cell depends on the type of electrolyte and electrodes used in the cell. The electromotive force or e.m.f. of a cell is the characteristic of the cell. It is different for different cells. It only depends on two factors: a) the type of electrolyte b) the material of electrodes For example, the e.m.f. of a Voltaic cell is 1.08 V and that of a Leclanche cell is 1.5 V.

#### The electric current flows in a direction opposite to the direction of flow of _______.

The electric currents flows from a region of higher potential to a region of lower potential, i.e., in a direction opposite to the direction of flow of electrons.

#### At the time of short circuit, the current in the circuit-

In short circuit, the resistance becomes almost negligible.

#### Electric current will stop flowing when the potential difference is

Electric current will stop flowing when the potential difference is zero. It means two ends are at the same potential.

#### Potential difference is measured using a _______

The instrument used to measure potential difference is Voltmeter.

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