Two material bars A and B of equal area of crosssection, are connected in series to a DC supply. A is made of usual resistance wire and B of an n-type semiconductor.
(i) In which bar is drift speed of free electrons greater?
(ii) If the same constant current continues to flow for a long time, how will the voltage drop across A and B be affected?
Justify each error.
(i) In which bar is drift speed of free electrons greater?
(ii) If the same constant current continues to flow for a long time, how will the voltage drop across A and B be affected?
Justify each error.
(a) Drift speed in B (n-type semiconductor) is higher
Reason : I = neAvd is same for both n is much lower in semiconductors.
(b) Voltage drop across A will increase as the resistance of A increases with increase in temperature. Voltage drop across B will decrease as resistance of B will decrease with increase in temperature.
Reason : I = neAvd is same for both n is much lower in semiconductors.
(b) Voltage drop across A will increase as the resistance of A increases with increase in temperature. Voltage drop across B will decrease as resistance of B will decrease with increase in temperature.
First a set of n equal resistors of R each is connected in series to a battery of emf E and internal resistance R. A current I is observed to flow. Then the n resistors are connected in parallel to the same battery. It is observed that the current becomes 10 times. What is n ?
A battery of emf E and internal resistance, r, when connected with an external resistance of 12Ω produces a current of 0.5 A. When connected across a resistance of 25Ω, it produces a current of 0.25 A. Determine
(i) the emf and (ii) the internal resistance of the cell.
A resistance of R Ω draws current from a potentiometer. The potentiometer has a total resistance \(R_0\) Ω as shown in the Fig below. A voltage V is supplied to the potentiometer. Derive an expression for the voltage across R when the sliding contact is in the middle of the potentiometer.
A battery of emf 10 V and internal resistance 3 ohm is connected to a resistor. If the current in the circuit is 0.5 A, find :
(i) the resistance of the resistor;
(ii) the terminal voltage of the battery.
In a Wheatstone bridge, three resistors P,Q, R are connected in three arms in order and 4th arm of resistance, s, is formed by two resistors s1 and s2 connected in parallel. The condition for bridge to be balanced is, P/Q
Draw a plot showing the variation of resistivity of a (i) conductor and (ii) semiconductor, with the increase in temperature. How does one explain this behaviour in terms of number density of charge carriers and the relaxation time ?
Define relaxation time of the free electrons drifting in a conductor. How is it related to the drift velocity of free electrons ? Use this relation to deduce the expression for the electrical resistivity of the material.
(i) An electric dipole is kept first to the left and then to the right of a negatively charged infinite plane sheet having a uniform surface charge density. The arrows p₁ and p₂ show the directions of its electric dipole moments in the two cases.
(i) When an ac source is connected to an ideal inductor shows that the average power supplied by the source over a complete cycle is zero.
(ii) A lamp is connected in series with an inductor and an ac source. What happens to the brightness of the lamp when the key is plugged in and an iron rod is inserted inside the inductor ? Explain.
(i) Find the value of the phase difference between the current and the voltage in the series LCR circuit shown below. Which one leads in phase : current or voltage ?
(ii) Without making any other change, find the value of the additional capacitor C₁, to be connected in parallel with the capacitor C, in order to make the power factor of the circuit unity.
Two material bars A and B of equal area of crosssection, are connected in series to a DC supply. A is made of usual resistance wire and B of an n-type semiconductor.
(i) In which bar is drift speed of free electrons greater?
(ii) If the same constant current continues to flow for a long time, how will the voltage drop across A and B be affected?
Justify each error.
(a) Define the term ‘conductivity’ of a metallic wire. Write its SI unit.
(b) Using the concept of free electrons in a conductor, derive the expression for the conductivity of a wire in terms of number density and relaxation time. Hence obtain the relation between current density and the applied electric field E.
In the two electric circuits shown in the figure, determine the readings of ideal ammeter (A) and the ideal voltmeter (V).
(i) When an ac source is connected to an ideal capacitor show that the average power supplied by the source over a complete cycle is zero.
(ii) A lamp is connected in series with a capacitor.Predict your observation when the system is connected first across a dc and then an ac source.What happens in each case if the capacitance of the capacitor is reduced ?