Electricity

A wire of uniform circular cross-section is replaced in an electrical circuit.

The new wire has the same length and same resistance, but half the diameter of the old wire. What is the ratio $$\frac{resistivity\ of\ the\ old\ wire}{resistivity\ ofthe\ old\ wire}?$$

A circuit is formed by connecting a resistor between the terminals of a battery of electromotive force (emf) 6 V. The battery has internal resistance. Which statement is correct when 1 C of charge flows around the complete circuit?

Four resistors are connected as shown.

What is the total resistance between X and Y?

An electric dipole consists of a positive and a negative charge separated by a fixed distance. The electric field due to the dipole is shown in the diagram below.

An electric force acts on an electron at point P.

In which direction does this force act?

What is the definition of electric current?

Two cylindrical copper wires, W₁ and W₂ , are held at the same temperature. W₂ is twice as long and has half the diameter of W₁

What is the ratio $$\frac{resis\tan ce\ of\ w\ _2}{resis\tan ce\ of\ w\ _1}?$$

A cylindrical resistor of volume V and length l has resistance R. The resistor has a uniform circular cross-section. What is the resistivity of the material from which the resistor is made?

The graph shows the variation of current I with the potential difference V in a device.

What is the resistance of the device at point P?

A lamp is connected to an electric cell and it lights at its working voltage. The lamp is then connected to the same cell in a circuit with an ideal ammeter and an ideal voltmeter. Which circuit allows the lamp to light at the original brightness?

A positive point charge P and a negative point charge Q of equal magnitude are held at fixed positions. Y is midway between P and Q.

Which of the following gives the direction of the electric field due to the charges at X, Y and Z?