Question
An AC source is connected to a diode and a resistor in series. Is the current thorough the resistor AC or DC?
✓
Answer
If the diode and resistor are in series, for the positive half cycle of AC, the current through the resistor will be DC. But for the next half cycle the current through the resistor will be zero. As a diode is a device that converts AC into DC, current through the resistor will be DC.
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Cathode rays constitute a stream of:
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- Positive ions.
- Negative ions.
A simple pendulum of length I is suspended from the ceiling of a car moving with a speed v on a circular horizontal road of radius r.
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A uniform magnetic field of 0.20 × 10-3 T exists in the space. Find the change in the magnetic scalar potential as one moves through 50cm along the field.
Read the passage given below and answer the following questions from 1 to 5.
When an object is in motion, its position changes with time. But how fast is the position changing with time and in what direction? To describe this, we define the quantity average velocity. Average velocity is defined as the change in position or displacement (△x) divided by the time intervals (△t), in which the displacement occurs:
$\text{V}=\frac{\text{x2}-\text{x1}}{\text{t2}-\text{t1}}=\frac{\triangle\text{x}}{\triangle\text{t}}$
Where x2 and x1 are the positions of the object at time t2and t1, respectively. The SI unit for velocity is m/s or m s–1, although km h–1 is used in many everyday applications. Like displacement, average velocity is also a vector quantity. Average speed is defined as the total path length travelled divided by the total time interval during which the motion has taken place:
Average speed = Total path length/ Total time interval.
Average speed has obviously the same unit (m s–1) as that of velocity. But it does not tell us in what direction an object is moving. Thus, it is always positive (in contrast to the average velocity which can be positive or negative). If the motion of an object is along a straight line and in the same direction, the magnitude of displacement is equal to the total path length.
The velocity at an instant is defined as the limit of the average velocity as the time interval Dt becomes infinitesimally small. In other words
$\text{V}=\lim_{\text{dt}-0}\frac{\text{dx}}{\text{dt}}$
$\text{V}=\frac{\text{dx}}{\text{dt}}$
Note that for uniform motion, velocity is the same as the average velocity at all instants. Instantaneous acceleration is defined in the same way as the instantaneous velocity
$\text{A}=\lim_{\text{dt}-0}\frac{\text{dv}}{\text{dt}}$
$\text{A}=\frac{\text{dv}}{\text{dt}}$
→When an object is in motion, its position changes with time. But how fast is the position changing with time and in what direction? To describe this, we define the quantity average velocity. Average velocity is defined as the change in position or displacement (△x) divided by the time intervals (△t), in which the displacement occurs:
$\text{V}=\frac{\text{x2}-\text{x1}}{\text{t2}-\text{t1}}=\frac{\triangle\text{x}}{\triangle\text{t}}$
Where x2 and x1 are the positions of the object at time t2and t1, respectively. The SI unit for velocity is m/s or m s–1, although km h–1 is used in many everyday applications. Like displacement, average velocity is also a vector quantity. Average speed is defined as the total path length travelled divided by the total time interval during which the motion has taken place:
Average speed = Total path length/ Total time interval.
Average speed has obviously the same unit (m s–1) as that of velocity. But it does not tell us in what direction an object is moving. Thus, it is always positive (in contrast to the average velocity which can be positive or negative). If the motion of an object is along a straight line and in the same direction, the magnitude of displacement is equal to the total path length.
The velocity at an instant is defined as the limit of the average velocity as the time interval Dt becomes infinitesimally small. In other words
$\text{V}=\lim_{\text{dt}-0}\frac{\text{dx}}{\text{dt}}$
$\text{V}=\frac{\text{dx}}{\text{dt}}$
Note that for uniform motion, velocity is the same as the average velocity at all instants. Instantaneous acceleration is defined in the same way as the instantaneous velocity
$\text{A}=\lim_{\text{dt}-0}\frac{\text{dv}}{\text{dt}}$
$\text{A}=\frac{\text{dv}}{\text{dt}}$
- For uniform motion instantaneous velocity is same as:
- Average velocity
- Average acceleration
- Instantaneous speed
- None of these
- If velocity is constant then
- Acceleration is zero
- Acceleration is positive
- Acceleration is negative
- None of these
- Define average speed
- Define instantaneous acceleration
- Define average velocity
Read the passage given below and answer the following questions from 1 to 5.
When a body is subjected to a deforming force, a restoring force is developed in the body. This restoring force is equal in magnitude but opposite in direction to the applied force. The restoring force per unit area is known as stress. If F is the force applied normal to the cross–section and A is the area of cross section of the body.
Magnitude of the stress $=\frac{\text{F}}{\text{A}}$
The SI unit of stress is N-m-2 or Pascal (Pa) and its dimensional formula is [ML-1 T-2]. The restoring force per unit area in this case is called tensile stress. If the cylinder is compressed under the action of applied forces, the restoring force per unit area is known as compressive stress. Tensile or compressive stress can also be termed as longitudinal stress. In both the cases, there is a change in the length of the cylinder. The change in the length ΔL to the original length L of the body is known as longitudinal strain.
The restoring force per unit area developed due to the applied tangential force is known as tangential or shearing stress.
→When a body is subjected to a deforming force, a restoring force is developed in the body. This restoring force is equal in magnitude but opposite in direction to the applied force. The restoring force per unit area is known as stress. If F is the force applied normal to the cross–section and A is the area of cross section of the body.
Magnitude of the stress $=\frac{\text{F}}{\text{A}}$
The SI unit of stress is N-m-2 or Pascal (Pa) and its dimensional formula is [ML-1 T-2]. The restoring force per unit area in this case is called tensile stress. If the cylinder is compressed under the action of applied forces, the restoring force per unit area is known as compressive stress. Tensile or compressive stress can also be termed as longitudinal stress. In both the cases, there is a change in the length of the cylinder. The change in the length ΔL to the original length L of the body is known as longitudinal strain.
The restoring force per unit area developed due to the applied tangential force is known as tangential or shearing stress.
- Restoring force per unit area is called as:
- Stress
- Strain
- Modulus of elasticity
- None of these
- Ratio of change in dimension to original dimension is called:
- Stress
- Strain
- Modulus of elasticity
- None of these
- Define shear stress.
- Define stress. Give its SI unit and dimension.
- Define strain. Give its SI unit and dimension
The plate current in a triode valve is zero. The temperature of the filament is high. It is possible that:
- Vg > 0, Vp > 0
- Vg > 0, Vp < 0
- Vg < 0, Vp > 0
- Vg < 0, Vp < 0
In a microwave oven, the food is kept in a plastic container and the microwave is directed towards the food. The food is cooked without melting or igniting the plastic container. Explain.
Explain why?
(a) The angle of contact of mercury with glass is obtuse, while that of water with glass is acute.
(b) Water on a clean glass surface tends to spread out while mercury on the same surface tends to form drops. (Put differently, water wets glass while mercury does not.)
(c) Surface tension of a liquid is independent of the area of the surface.
(d) Water with detergent dissolved in it should have small angles of contact.
(e) A drop of liquid under no external forces is always spherical in shape.
(a) The angle of contact of mercury with glass is obtuse, while that of water with glass is acute.
(b) Water on a clean glass surface tends to spread out while mercury on the same surface tends to form drops. (Put differently, water wets glass while mercury does not.)
(c) Surface tension of a liquid is independent of the area of the surface.
(d) Water with detergent dissolved in it should have small angles of contact.
(e) A drop of liquid under no external forces is always spherical in shape.
Why do marine animals live deep inside a lake when the surface of the lake freezes?