Physics In Life Chapter 25 Full Anwser
Chapter 25 Electrical Power and Domestic Electricity
Checkpoint (p.197)
1. The heating effect of current increases with the applied voltage across the wire.
Microscopically, when a voltage is applied across the ends of a metal wire, an electric field is set up between the ends. The free electrons are accelerated by the field and collide frequently with the metal ions in the wire. Thus, some energy is transformed into the internal energy of the wire.
When the applied voltage increases, the electric field is stronger. The electrons collide harder as well as more frequently with the ions. Thus, more energy is transformed into the internal energy.
2. The heating element is usually wound into a coil to facilitate heat transfer from the heating element to the targeted area. The coiling of the heating element results in a long enough wire that gives a reasonable resistance. This is to protect the source against short circuit.
3. No. The resistance of a copper wire is much smaller than that of a Nichrome wire of the same length. If we replace the wire with a copper wire, the battery will be short-circuited and become very hot in a short time. It may even explode.
Checkpoint (p.200)
1. (a) The equation defines the average electrical power P as the amount of electrical energy E transformed in a time interval t. It is applicable (but not restricted) to all kinds of electrical energy transformation.
(b) The equation defines the electrical power P supplied to or dissipated by an electrical component. When the voltage across the component is V and the current flowing through the component is I, the electrical power P = VI.
The equation is applicable to all kinds of electrical components.
(c) The equation defines the electrical power P supplied by a source. When a source of e.m.f. ε delivers a current I to a component, the power supplied
P = εI. The equation is applicable to sources only.
(d) The power P dissipated by a resistor of resistance R is given
Checkpoint (p.197)
1. The heating effect of current increases with the applied voltage across the wire.
Microscopically, when a voltage is applied across the ends of a metal wire, an electric field is set up between the ends. The free electrons are accelerated by the field and collide frequently with the metal ions in the wire. Thus, some energy is transformed into the internal energy of the wire.
When the applied voltage increases, the electric field is stronger. The electrons collide harder as well as more frequently with the ions. Thus, more energy is transformed into the internal energy.
2. The heating element is usually wound into a coil to facilitate heat transfer from the heating element to the targeted area. The coiling of the heating element results in a long enough wire that gives a reasonable resistance. This is to protect the source against short circuit.
3. No. The resistance of a copper wire is much smaller than that of a Nichrome wire of the same length. If we replace the wire with a copper wire, the battery will be short-circuited and become very hot in a short time. It may even explode.
Checkpoint (p.200)
1. (a) The equation defines the average electrical power P as the amount of electrical energy E transformed in a time interval t. It is applicable (but not restricted) to all kinds of electrical energy transformation.
(b) The equation defines the electrical power P supplied to or dissipated by an electrical component. When the voltage across the component is V and the current flowing through the component is I, the electrical power P = VI.
The equation is applicable to all kinds of electrical components.
(c) The equation defines the electrical power P supplied by a source. When a source of e.m.f. ε delivers a current I to a component, the power supplied
P = εI. The equation is applicable to sources only.
(d) The power P dissipated by a resistor of resistance R is given