Đề kiểm tra đổi tuyển

BÀI KIỂM TRA DẠNG 4.
1. Có hai bóng đèn: Đ1(110V- 60W) và Đ2(110V-100W) và trở.
a) Mắc tiếp hai bóng vào hiệu điện thế 110V đèn nào sáng hơn?
b) Hãy vẽ hai sơ đồ mạch điện ( sao cho dòng điện chỉ chạy qua một phần của biến trở ) để hai đèn có thể sáng bình thường khi mắc vào nguồn điện 220V ? Tính điện trở của biến trở khi đó ?
2. Cho mạch điện như hình vẽ, trên các bóng đèn có ghi: Đ1 (12V - 6W); Đ2 (12V - 12W). Trên đèn Đ3 chỉ ghi 3W, giá trị hiệu điện thế định mức bị mờ hẳn.
Mạch đảm bảo các đèn sáng bình thường.
a) Hãy tính hiệu điện thế định mức của đèn Đ3.
b) Cho biết R4 = 9Ω, hãy tính R4 ?
c) Tính hiệu suất của mạch điện ( xem công suất trên hai điện trở là hao phí ) ?
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