Phòng GD & ĐT Ngọc Lặc ĐỀ THI THỬ HSG CẤP HUYỆN
Trường THCS Phúc Thịnh Môn: Vật lí 7.( Thời gian làm bài 120 phút )
Họ và tên......................................

ĐỀ BÀI
Câu 1( 2 điểm): Giải thích tại sao ta nhìn thấy bóng của cái cây trên mặt hồ nước phẳng lại lộn ngược so với cây?
Câu 2( 3 điểm): Khi có hiện tượng nhật thực và hiện tượng nguyện thực thì vị trí tương đối của mặt trăng, mặt trời và trái đất như thế nào?
Câu 3(3 điểm): Vào mùa đông nhất là những ngày thời tiết hanh khô cởi áo len ta thường thấy tiếng nổ lét đét nhỏ, nếu cởi vào ban đêm ta còn thấy sự phóng các tia lửa điện. hãy giải thích hiện tượng trên?
câu 4(2 điểm): Tại sao khi trang điểm người ta không dùng gương cầu lồi hay gương cầu lõm mà lại dùng gương phẳng?
Câu 5(3 điểm): Cho một mũi tên AB đặt vuông góc với một gương phẳng, điểm A nằm trên gương.
a. Vẽ ảnh của mũi tên AB tạo bởi gương phẳng?
b. Vẽ một tia sáng từ B xuống gương và tia phản xạ của nó?
c. phải đặt AB thế nào để có ảnh của AB song song cùng chiều vói AB?
Câu 6(2 điểm): Để có tiếng vang trong môi trường không khí thì thời gian kể từ khi âm phát ra đến khi nhận âm phản xạ phải lớn hơn 1/15 giây. khoảng cách giữa người và tường phải có giá trị là bao nhiêu thì nghe được tiếng vang ( biết vận tốc âm trong kk là 340m/s)
Câu 7(2 điểm): Cho hai bống đèn Đ1 và Đ2 mắc nối tiếp nhau,một ampekế, một khoá k đang mở.vôn kế V1 đo hiệu điện thế hai đầu Đ1, vôn kế V2 đo hiệu điện thê hai đầu Đ2, vôn kế V3 đo hiệu điện thê hai đầu nguồn điện.
a. Vẽ sơ đồ mạch điện?
b. Vôn kế V1 chỉ 2,5 ampe, vôn kế V2 chỉ gấp 3 lần V1.tìm số chỉ V3 ?
Câu 8(3điểm): Hãy giải thích hoạt động của cái còi ( loại còi bên trong có một viên bi )


PHẦN BÀI LÀM CỦA THÍ SINH
........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................... ...........................
.............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
...................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
.............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
......................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
.............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
....................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................