1SEE Boardqb-q0
What is direct current (d.c.)?
Ans.: Direct current is current that flows in only one fixed direction.
Every question in this chapter, answered and explained — step-by-step solutions drawn live from the chapter library across 7 question sections.
What is direct current (d.c.)?
What is alternating current (a.c.)?
What is the frequency of a.c. used in Nepal?
Who discovered the magnetic effect of electric current?
What is a solenoid?
What is magnetic flux?
What is the SI unit of magnetic flux?
What is the motor effect?
Who discovered electromagnetic induction?
What is a transformer?
On which principle does a transformer work?
Name two sources of d.c.
Name two sources of a.c.
What is a rectifier used for?
What is core lamination?
What is the magnetic effect of current?
State Maxwell's right-hand thumb rule.
State Maxwell's right-hand grip rule for a solenoid.
Write two factors affecting the strength of the magnetic field of a solenoid.
Write two uses of a solenoid.
State Faraday's law of electromagnetic induction.
What is electromagnetic induction?
Write two ways to increase the current produced by a dynamo.
What is mutual induction?
Why is the transformer core laminated?
When a ceiling fan is connected to the circuit of a solar panel, the fan does not rotate.
When a magnetic compass is placed near a circuit in which an electric current is flowing, its needle deflects.
An electromagnet is used in the electric bell.
The number of primary windings and secondary windings of a transformer are not the same.
The core of a transformer is laminated.
Transformers are used in mobile chargers.
Difference Between a.c. and d.c.
| Alternating Current (a.c.) | Direct Current (d.c.) |
|---|---|
| Direction changes periodically. | Direction remains fixed. |
| Produced by dynamo/a.c. generator. | Produced by dry cell/battery/solar panel. |
| Has a non-zero frequency (50 Hz in Nepal). | Frequency is zero. |
Difference Between Dynamo and Generator
| Dynamo | Generator |
|---|---|
| Produces current on a small scale. | Produces current on a large scale. |
| Used in bicycles, motorcycles. | Used in power plants for domestic/industrial supply. |
| Usually simple in construction. | Complex construction with turbines and large coils. |
Difference Between Motor and Generator
| Motor | Generator |
|---|---|
| Converts electrical energy into mechanical energy. | Converts mechanical energy into electrical energy. |
| Works on the motor effect. | Works on electromagnetic induction. |
| Needs an electric supply to run. | Needs mechanical rotation (e.g., turbine) to run. |
Difference Between Step-Up and Step-Down Transformer
| Step-Up Transformer | Step-Down Transformer |
|---|---|
| Secondary turns more than primary turns. | Secondary turns fewer than primary turns. |
| Output voltage higher than input voltage. | Output voltage lower than input voltage. |
| Used to send electricity through transmission lines. | Used to supply usable low voltage to consumers/appliances. |
Draw the magnetic field lines around a current-carrying straight wire and a solenoid, and explain.
Around a solenoid, the field is similar to that of a bar magnet — strong and nearly uniform inside, emerging from one end (North Pole) and entering the other end (South Pole), and weak in the middle outside the coil.
Explain the working of a simple electric motor based on the motor effect.
What is electromagnetic induction? Explain the factors affecting the magnitude of induced e.m.f.
The magnitude of the induced e.m.f. depends on: 1) the strength of the magnetic field, 2) the number of turns in the coil, and 3) the speed at which the magnetic flux changes (rate of relative motion). Moving a magnet quickly in and out of a coil induces more voltage than moving it slowly.
Describe the construction and working principle of a transformer.
The ratio of the number of primary turns to secondary turns determines whether the transformer is step-up or step-down, following the formula Np/Ns = Vp/Vs. Since mutual induction requires a changing current, a transformer only works with a.c., not d.c.
To charge a laptop of 20V, a charger with 550 primary turns is connected to an a.c. source of 220V. Calculate the number of secondary windings.
Given: Vp = 220 V, Vs = 20 V, Np = 550
The number of secondary windings of a transformer used in a microwave oven is 10 times the number of windings in the primary coil. If it is connected to a source of 220V, what is the secondary voltage obtained?
Given: Vp = 220 V, Ns : Np = 10 : 1
The ratio of primary winding to secondary winding of a transformer is 22:1. If an adapter with that transformer is connected to a 220V supply, calculate the output voltage.
Given: Vp = 220 V, Np : Ns = 22 : 1
Additional SEE Practice — Q4. A transformer has 100 turns in the primary coil and 25 turns in the secondary coil. If the primary voltage is 220V, find the secondary voltage and state the type of transformer.
Given: Np = 100, Ns = 25, Vp = 220 V
Draw and label the block diagrams of a step-up and a step-down transformer.
In a step-up transformer, the primary coil has fewer turns than the secondary coil, so the output voltage is higher (e.g., 110V primary, 220V secondary).
Study the diagram of electricity generation, transmission and distribution, and label transformer J and K in a power system (J near the power station, K near consumers).
In the picture, a bar magnet is introduced into a solenoid connected to a galvanometer. Explain what happens in each situation: (i) magnet introduced slowly, (ii) magnet introduced rapidly, (iii) magnet held stationary inside, (iv) magnet pulled out quickly.