Physics Electricity

Explanation

Microwaves are a form of electromagnetic radiation that have wavelengths varying from one meter to one millimeter, or frequencies between 300 MHz (0.3 GHz) and 300 GHz. Microwave ovens emit nonionizing microwave radiation at a frequency around 2.45 GHz to heat food through absorption of energy by water, fats, and sugars in the food. Bluetooth and Wi-Fi technologies are commonly used for networking, printing, and file transfer, operating within the 2.4 to 2.5 GHz frequency range. In the United States, cordless phones typically utilize the 1.9 GHz or 2.4 GHz frequency bands.

Explanation

Both statements A and R are correct, and statement R provides the correct explanation for statement A.

Explanation

In the case of a dry human body, the electric resistance is on the order of magnitude of 10⁴ ohms. However, when the body is wet due to water or sweat, the resistance decreases to around 1000 ohms.

Explanation

In this question, we have two statements. The first statement mentions that a geo-stationary satellite is located at a height of approximately 10,000 km. The second statement explains that FM transmission of music provides high quality due to its immunity to atmospheric or man-made noises that often cause frequency variations. The correct option is (b) 2 only, as only the second statement is accurate.

Explanation

In our houses, the flow of current in the AC electricity line switches direction 60 times every second. This is because the frequency of the alternating voltage supplied to our homes is 50 Hz. The correct option is that statement A is false but statement R is true.

Explanation

In this question, we are given that two wires have their lengths, diameters, and resistivities in the ratio of 1:2. If the resistance of the thinner wire is 10 ohms, we need to find the resistance of the thicker wire. By applying the formula for resistance (R = ρl/A), we can calculate that the resistance of both wires is equal. Therefore, the resistance of the thicker wire is also 10 ohms. So, the correct answer is option (b) 10 ohms.

Explanation

Fluorescent tubes are equipped with a choke coil, which is responsible for reducing the current in the circuit.

Explanation

A TV remote control unit uses radio waves to operate a TV set. Radio waves are a type of electromagnetic radiation that have longer wavelengths in the electromagnetic spectrum compared to infrared light.

Explanation

In a typical light bulb, a wire filament is heated by electrical resistance to produce light. The filament wire is not consistent in its composition. The bulb cannot be completely emptied of air. Additionally, the wires that support the filament are prone to melting at high temperatures. All three statements are accurate in explaining why an ordinary light bulb has a relatively short lifespan.

Explanation

In the case of a motor car battery, it typically has a voltage of 12 volts. The electrolyte commonly used is hydrochloric acid, while the electrodes are made of lead and copper. The capacity of the battery is measured in terms of ampere-hour. A correct statement would be that the voltage is usually 12 V and the capacity is expressed in ampere-hour, making option (d) - 1 and 4 correct.

Explanation

In mains electric supply, a fuse is an important safety device. It contains a metal wire or strip that melts when there is an excessive flow of current. It is crucial for the fuse to have a low melting point so that it can melt in the event of a short-circuit or overloading, acting as a sacrificial overcurrent protection device.

Explanation

When an electric current flows through a metal wire, its temperature increases. This is because the metal atoms collide with each other, causing the release of heat energy. This explanation supports the assertion that the rise in temperature is due to the collision of metal atoms. So, option (a) is correct.

Explanation

Iron exhibits ferromagnetic behavior, hydrogen is diamagnetic, oxygen displays paramagnetic properties, and nitrogen is also diamagnetic. Therefore, among the options provided, oxygen is the element that is paramagnetic in nature.

Explanation

A transformer is a device that is beneficial for increasing or decreasing voltages. It is used in AC circuits, not DC circuits. The correct option is (c) where A is true but R is false.

Explanation

In domestic electrical wiring, the most common type of connection used is parallel connection. This means that the voltage across each device or appliance remains constant, and the total current flowing through the circuit is the combined sum of the currents passing through each individual component.

Explanation

In television broadcasts, the technique used to transmit audio signals is known as frequency modulation. This process involves varying the frequency of the carrier signal based on the instantaneous value of the modulating voltage.