Question

Напряжение в бортовой сети автомобиля 12 В. Какую мощность имеет лампочка стоп-сигнала, если ее сопротивление 7 Ом ? В сеть с напряжением 100 В включена спираль, сопротивление которой 20 Ом. Чему равна сила тока в спирали? Чему равно удельное сопротивление фехраля ,если в проволоке длиной 3м и площадью сечения 0,25 мм², изготовленной из этого материала, течет ток силой 2А при напряжении на концах проволоки 31,2 В? Резисторы на 8 кОм и 1 кОм соединены последовательно. Определите показания вольтметра на крайних точках соединения, если сила тока в цепи равна 3 мА. Что покажут вольтметры, подключенные к первому и второму резисторам? В калориметр с 100 г воды опущена спираль сопротивлением 5 Ом. Сила тока в ней - 2.5 А. На сколько градусов согреется вода за 5 минут?

Answer 1

1)
P=U^2/R =12^2/7 =20.5 Вт

2)
I=U/R =100/20 =5 A

3)
p=R*S/L
R=U/I =31.2/2= 15.6 Ом
p=15.6*0.25/3= 1.3 Ом*мм^2/м
 

4)
U= I*R =I*(R1+R2) =0.003*(8000+1000) =27 B напряжение на крайних точках
U1= I*R1= 0.003*8000 =24 B показания на 1 резисторе
U2 = U-U1= 27-24=3 B показания на 2 резисторе

5)
t=5 мин =300 c
c=4200 Дж/кг*С
м=100 г=0,1кг

Q= I^2*R*t
Q=2.5^2*5*300=9375 Дж
Q=c*m*(tk-tн)
t=Q/c*m=9375/4200*0.1=22.3 гр

Answer 2

Calculation of Power in a Stop Signal Lamp

The voltage in the car's onboard network is 12 V. To calculate the power of the stop signal lamp, we need to use Ohm's law, which states that power (P) is equal to the square of the current (I) multiplied by the resistance (R). The formula is as follows:

P = I^2 * R

Given that the resistance of the stop signal lamp is 7 Ω, we can calculate the power as follows:

P = (I^2) * 7

However, we need to find the current (I) first. To do this, we can use Ohm's law, which states that current (I) is equal to voltage (V) divided by resistance (R). The formula is as follows:

I = V / R

Substituting the given values, we can calculate the current:

I = 12 V / 7 Ω

Now that we have the current, we can calculate the power:

P = (I^2) * 7

Let's calculate the power of the stop signal lamp.

P = (12 V / 7 Ω)^2 * 7 Ω

Using a calculator, we find that the power of the stop signal lamp is approximately 20.57 W.

Calculation of Current in a Spiral with a Resistance of 20 Ω

In a circuit with a voltage of 100 V and a spiral with a resistance of 20 Ω, we can calculate the current using Ohm's law:

I = V / R

Substituting the given values, we can calculate the current:

I = 100 V / 20 Ω

Using a calculator, we find that the current in the spiral is 5 A.

Calculation of Specific Resistance of FeCrAl

To calculate the specific resistance of FeCrAl, we need to use Ohm's law, which states that resistance (R) is equal to voltage (V) divided by current (I). The formula is as follows:

R = V / I

Given that the length of the wire is 3 m, the cross-sectional area is 0.25 mm², the current is 2 A, and the voltage across the wire is 31.2 V, we can calculate the specific resistance as follows:

R = (31.2 V) / (2 A)

Using a calculator, we find that the specific resistance of FeCrAl is approximately 15.6 Ω/m².

Calculation of Voltmeter Readings in a Series Circuit

In a series circuit with resistors of 8 kΩ and 1 kΩ connected in series, and a current of 3 mA, we can calculate the voltmeter readings at the extreme points of the connection.

To calculate the voltage across each resistor, we can use Ohm's law:

V = I * R

For the 8 kΩ resistor:

V1 = (3 mA) * (8 kΩ)

For the 1 kΩ resistor:

V2 = (3 mA) * (1 kΩ)

Using a calculator, we find that the voltmeter readings at the extreme points of the connection are approximately 24 V and 3 V respectively.

Voltmeter Readings for the First and Second Resistors

If voltmeters are connected to the first and second resistors in the circuit, they will measure the voltage across each resistor.

The voltmeter connected to the first resistor will measure the voltage drop across the 8 kΩ resistor, which is approximately 24 V.

The voltmeter connected to the second resistor will measure the voltage drop across the 1 kΩ resistor, which is approximately 3 V.

Calculation of Temperature Increase in Water

In a calorimeter containing 100 g of water, a spiral with a resistance of 5 Ω is immersed. The current flowing through the spiral is 2.5 A. We need to calculate the temperature increase in the water after 5 minutes.

To calculate the energy transferred to the water, we can use the formula:

Q = I^2 * R * t

Where: - Q is the energy transferred (in joules) - I is the current (in amperes) - R is the resistance (in ohms) - t is the time (in seconds)

Given that the current is 2.5 A, the resistance is 5 Ω, and the time is 5 minutes (or 300 seconds), we can calculate the energy transferred:

Q = (2.5 A)^2 * 5 Ω * 300 s

Using a calculator, we find that the energy transferred to the water is approximately 9375 J.

The temperature increase in the water can be calculated using the specific heat capacity of water, which is approximately 4.18 J/g°C. The formula is:

ΔT = Q / (m * c)

Where: - ΔT is the temperature increase (in °C) - Q is the energy transferred (in joules) - m is the mass of the water (in grams) - c is the specific heat capacity of water (in J/g°C)

Given that the mass of the water is 100 g and the specific heat capacity of water is 4.18 J/g°C, we can calculate the temperature increase:

ΔT = 9375 J / (100 g * 4.18 J/g°C)

Using a calculator, we find that the temperature increase in the water is approximately 22.4°C.